metadata: authors: 0: author: Zuffinetti,Guillaume
1: author: Meunier,Simon
count: Africa,World
docna: 0: docna: Mapping the Risk Posed to
            Groundwater-Dependent Ecosystems by Uncontrolled Access to
            Photovoltaic Water Pumping in Sub-Saharan Africa
docty: Policy Research Working Paper
theme: Water Institutions, Policies and Reform,Mitigation,Environment and Natural Resource Management,Water Resource Management,Climate change,Adaptation
abstracts: cdata!: Photovoltaic-powered groundwater pumping
            offers a transformative solution for water services in
            underserved areas. However, without proper regulation, this
            technology could overexploit groundwater resources,
            threatening the groundwater-dependent ecosystems that rely
            on them. Often overlooked in development planning and water
            allocation, groundwater-dependent ecosystems hold
            significant socioeconomic and environmental importance. This
            study maps the risk to groundwater-dependent ecosystems in
            Sub-Saharan Africa from uncontrolled access to photovoltaic
            groundwater pumping using the analytic hierarchy process. It
            evaluates risks using data on irradiance, groundwater, and
            population, and novel data on groundwater-dependent
            ecosystems. Two scenarios are analyzed to improve the
            robustness of the findings. The results show that 92 percent
            of Sub-Saharan Africa&#x2019;s groundwater-dependent
            ecosystems risk overexploitation if photovoltaic water
            pumping is implemented without proper controls.
            Groundwater-dependent ecosystems in Southern and Eastern
            Africa, particularly in South Africa and Namibia, are found
            to face higher risks, while those in Gabon, the Republic of
            Congo, and southern Nigeria tend to be less at risk.
            Comparing these results with populations relying on
            unimproved water sources highlights regions like southern
            Nigeria and South Sudan, which could be prioritized for
            potential photovoltaic water pumping system investments due
            to their higher groundwater development needs and lower
            risks to groundwater-dependent ecosystems. Conversely, areas
            like Namibia and South Africa, with lower groundwater
            development needs but higher risks to groundwater-dependent
            ecosystems, should require targeted investments and very
            close groundwater monitoring. These findings can help policy
            makers in targeting investments in photovoltaic water
            pumping systems and identifying regions needing careful
            monitoring to ensure sustainable groundwater use and minimal
            impact on groundwater-dependent ecosystems.
display_title: Mapping the Risk Posed to
            Groundwater-Dependent Ecosystems by Uncontrolled Access to
            Photovoltaic Water Pumping in Sub-Saharan Africa
listing_relative_url: /research/2024/09/34396967/mapping-risk-posed-groundwater-dependent-ecosystems-uncontrolled-access-photovoltaic-water-pumping-sub-saharan-africa
topicv3: Environmental Sustainability m1325984 1786,Solar Energy m1326390 528,Ecosystems m1326634 590,Groundwater Irrigation m1504478 3679
publishtoextweb_dt: 2024-09-30T00:00:00Z
dois: 10.1596/1813-9450-10935
origu: Off of Sr VP Dev Econ/Chief Econ (DECVP)
no_of_pages: 14
author_keys: 0: author_key: NA
1: author_key: NA
model_extractions: Policy Research Working Paper 10935 Mapping the Risk Posed to Groundwater-Dependent Ecosystems by Uncontrolled Access to Photovoltaic Water Pumping in Sub-Saharan Africa _Guillaume Zuffinetti Simon Meunier_ Water Global Practice September 2024 A verified reproducibility package for this paper is available at http://reproducibility.worldbank.org, click **here** for direct access.
Policy Research Working Paper 10935

# **Abstract**

Photovoltaic-powered groundwater pumping offers a transformative solution for water services in underserved areas. However, without proper regulation, this technology could overexploit groundwater resources, threatening the groundwater-dependent ecosystems that rely on them. Often overlooked in development planning and water allocation, groundwater-dependent ecosystems hold significant socioeconomic and environmental importance. This study maps the risk to groundwater-dependent ecosystems in Sub-Saharan Africa from uncontrolled access to photovoltaic groundwater pumping using the analytic hierarchy process. It evaluates risks using data on irradiance, groundwater, and population, and novel data on groundwater-dependent ecosystems. Two scenarios are analyzed to improve the robustness of the findings. The results show that 92 percent of Sub-Saharan Africa’s groundwater-dependent ecosystems risk overexploitation if photovoltaic water pumping is implemented without proper controls. Groundwater-dependent ecosystems in Southern and Eastern Africa, particularly in South Africa and Namibia, are found to face higher risks, while those in Gabon, the Republic of Congo, and southern Nigeria tend to be less at risk. Comparing these results with populations relying on unimproved water sources highlights regions like southern Nigeria and South Sudan, which could be prioritized for potential photovoltaic water pumping system investments due to their higher groundwater development needs and lower risks to groundwater-dependent ecosystems. Conversely, areas like Namibia and South Africa, with lower groundwater development needs but higher risks to groundwater-dependent ecosystems, should require targeted investments and very close groundwater monitoring. These findings can help policy makers in targeting investments in photovoltaic water pumping systems and identifying regions needing careful monitoring to ensure sustainable groundwater use and minimal impact on groundwater-dependent ecosystems.

This paper is a product of the Water Global Practice. It is part of a larger effort by the World Bank to provide open access to its research and make a contribution to development policy discussions around the world. Policy Research Working Papers are also posted on the Web at http://www.worldbank.org/prwp. The authors may be contacted at simon.meunier@centralesupelec.fr. A verified reproducibility package for this paper is available at http://reproducibility. worldbank.org, click **here** for direct access.

<!-- Start of picture text --> TRANSPARENT<br>ANALYSIS<br>G<br>R E<br>N<br>S<br>I P<br>Y E<br>K A<br>C A<br>R P<br>LI R<br>O E<br>O C<br>W R<br>H<br>S<br>P<br><!-- End of picture text --> _The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent._ Produced by the Research Support Team
**Mapping the risk posed to groundwater-dependent ecosystems by the uncontrolled access to photovoltaic water pumping in sub-Saharan Africa**

Guillaume Zuffinetti<sup>1,2</sup> , Simon Meunier<sup>1,2, *</sup> _1 Université Paris-Saclay, CentraleSupélec, CNRS, GeePs, Gif-sur-Yvette 91192, France_ _2 Sorbonne Université, CNRS, GeePs, Paris 75252, France_

- _Corresponding author email address: simon.meunier@centralesupelec.fr_

_This paper is related to the World Bank report "The Hidden Wealth of Nations: The Economics of Groundwater in Times of Climate Change" (2023)_

**JEL codes:** Q25, Q42.

**Keywords** : Groundwater-dependent ecosystems, Photovoltaic water pumping systems, Analytic Hierarchy Process, Sustainable groundwater management, sub-Saharan Africa
# 1. Introduction

Expanding access to electricity and water are key development priorities, closely related in the regions where access gaps are most pronounced, such as in the case of Sub-Saharan Africa (SSA). The World Bank estimates that currently, 600 million people in SSA lack access to electricity, creating significant barriers to health care, education, productivity, digital inclusivity, and ultimately job creation (IEA, IRENA, UNSD, World Bank, WHO., 2024). Those barriers are compounded by a lack of access to clean water: 400 million people in SSA lack access to safely managed drinking water services (UNICEF, WHO, 2022). Progress in photovoltaic technologies has enabled a lowering of costs (Chandel et al., 2015; Global Solar Atlas, 2024) that can be a game changer in expanding access. Multilateral development partners such as the World Bank and the African Development Bank Group are partnering to provide at least 300 million people in Africa with electricity access by 2030. The expansion of photovoltaic energy at scale will also enable an expansion of solar pumping for irrigation.

This is promising for SSA where less than 5 percent of agricultural land is irrigated, and less than 7 percent of irrigated lands uses groundwater (Rodella, Zaveri and Bertone, 2023). This could also present challenges in terms of impacts on groundwater-dependent ecosystems (GDEs) and overexploitation if access to groundwater resources is not appropriately controlled, a scenario welldocumented in regions such as South Asia and the Middle East (Lezzaik et al., 2018; Mukherjee, 2018).

There is growing recognition of the importance of those GDEs, from their socio-economic to their environmental value, including for carbon storage (Esteban and Dinar, 2016; Mendonça et al. 2017; Murray et al., 2003, 2006; Rohde et al., 2024). For instance, Mendonça et al. (2017) estimate that perennial lakes, mainly GDEs, trap some 0.33 billion tons of CO2 per year, corresponding to about 1% of the present global CO2 emissions.

GDEs play a crucial role in supporting the livelihoods of some of the most vulnerable populations in Sub-Saharan Africa, such as pastoralists (Rohde et al., 2024). The role of GDEs can often be indirect, for instance, through the hydraulic lift provided by certain tree species. However, GDEs are not consistently identified and mapped on a large scale, especially in developing countries. This data gap is significant, as GDEs, particularly in arid regions, are highly susceptible to even minor fluctuations in groundwater levels, which can jeopardize their survival.

A new World Bank database of GDEs in Sub-Saharan Africa shows their diversity and importance to people living in poverty (Rodella, Zaveri and Bertone, 2023). The database was compiled using a wide range of sources reflecting local and academic knowledge and identifies more than 200 GDEs across four main geographic types—inland surface waters (riverine, lacustrine, and wetland ecosystems); coastal and marine ecosystems (coastal and near-shore marine ecosystems), terrestrial springs (near spring and springs influenced zone ecosystems; includes oases); and terrestrial vegetation (sparse vegetation ecosystems and forests and woodlands ecosystems).

This dataset allows for novel analysis of the potential impacts of intervention affecting groundwater directly and indirectly. For instance, water extraction from aquifers by pumping systems can lead to the overexploitation of groundwater resources and a decrease in groundwater storage, which can, in turn, cause a loss of discharge from groundwater to wetlands, springs, streams/rivers, or coastal areas (McCallum et al., 2013). In addition, a decline in groundwater storage can lead to a decrease in the water table (Wada et al., 2010), rendering groundwater inaccessible to terrestrial vegetation (Barron et al., 2014).

To the authors’ knowledge, this is the first paper looking at the potential impacts of the extension of photovoltaic water pumping systems (PVWPS) on GDEs. Even though several articles studied the suitability of photovoltaic water pumping systems (PVWPS) in different regions of sub-Saharan Africa (e.g., Gebrezgabher et al., 2021; Schmitter et al., 2018; Soenen et al., 2021; Xie et al., 2021), no article has investigated the risk posed to GDEs by the uncontrolled access to groundwater through photovoltaic water pumping across the continent. The potential to scale up shallow groundwater irrigation in the SSA region is undeniable and could be a game changer for poverty, food security, and climate adaptation (Rodella, Zaveri and Bertone, 2023). However, the analysis seeks to illuminate the unintended consequences of unfettered access and highlight the need for preventive measures to be in place prior to scaling up photovoltaic pumping.

In this article, we use the Analytic Hierarchy Process (AHP) to map the risk posed to sub-Saharan GDEs by an uncontrolled expansion of access to groundwater through photovoltaic pumping. More specifically, we evaluate the risk of over-exploitation for GDEs using mapped data on groundwater, irradiance, population, and GDEs. Section 2 details the datasets used in our analysis.

2
Section 3 outlines our methodology, followed by the presentation and discussion of results in Section 4. Section 5 covers the limitations of our study, while Section 6 explores the policy implications. Section 7 concludes the paper.

# 2. Data

The datasets used in this study are described in Table 1. These input datasets have different spatial resolution. For the subsequent sections of the article, we use the spatial resolution of the global horizontal irradiance (GHI) map, i.e., 0.2° (~22 km). We apply this resolution to all input datasets by nearest neighbour interpolation. The shape file on the type of GDEs is rasterized at this same resolution. Besides, we use irradiance data from 2020. In Figure 1, we plot the annual average of GHI for 2020, static water level, aquifer transmissivity, groundwater storage, population density, renewable groundwater resources and type of GDE across subSaharan Africa.

|**Data**|**Description**|**Unit**|**Spatial**<br>**resolution**|**Temporal resolution and**<br>**coverage**|**Year of**<br>**release**|<br>**Provider**|**Type of**<br>**data**|
|---|---|---|---|---|---|---|---|
|Global<br>Horizontal<br>Irradiance<br>(GHI)|Radiation received by a horizontal<br>plane from all directions.|W/m<sup>2</sup>|0.2°<br>~22 km|One temporal vector for each<br>location.<br>Data from 2005 to 2020 with<br>a time step of 30 min (some<br>datapoints are missing for<br>years 2005 to 2012).|<br>2021|European<br>Commission,<br>2021||
|Static water<br>level|Depth of water in the borehole when<br>there is no pumping.|m|0.0083°<br>~1 km||2013|Fan et al., 2013||
|Aquifer<br>transmissivity|Rate at which groundwater flows<br>horizontally through an aquifer|m<sup>2</sup>/day||||British<br>Geological||
|Groundwater<br>storage|Amount of water in the aquifer<br>defined as a water depth|m|0.05°<br>~6 km||2012|Survey (Bonsor<br>and<br>MacDonald,<br>2011;<br>Macdonald,<br>2012)|Raster<br>file<br>|
|Population<br>density|Number of inhabitants per square<br>kilometer|hab/km<sup>2</sup>|0.04°<br>~5 km|Dependence in time not<br>provided.|2020|Center for<br>International<br>Earth Science<br>Information<br>Network, 2018||
|Renewable<br>groundwater<br>resources|Volume of renewable groundwater<br>that can be abstracted per year|km<sup>3</sup>/yr|0.5°<br>~60 km|||||
|Type of GDE|• Inland surface waters<br>• Terrestrial springs<br>• Coastal and marine ecosystems<br>• Terrestrial vegetations|-|-||2022|World Bank|Shape<br>File|

_Table 1 – Input datasets._ 3
<!-- Start of picture text --> Wim?<br>40<br>280<br>20<br>2<br>£0 aa<br>-20 200<br>180<br>-37<br>-20 0 20 40 54<br>longitude . (°)<br><!-- End of picture text --> <!-- Start of picture text --> 40<br>ee “Sa<br>Ox .<br>(5) . 4<br>0.1-0.5 m/d XO<br>M)1-smyd wa<br>9 | MES- 10 ma a: -<br>i 10-s0m%d p<br>50<br>Hi 500 -- 501 0 00ma md sy<br>37<br>-20 0 20 40 54<br>longitude (°)<br><!-- End of picture text -->

<!-- Start of picture text --> hab/km?<br>40 105<br>,<br>~ .<br>2 : % - 103<br>Zz bs<br>2 x be leg: 102<br>a F beei!<br>“SS ag<br>iy ae<br>-20 ~—<br>2 3i ig 10!<br>26<br>37 > <10°<br>-20 0 longitude_ 20 (°) 40 54<br><!-- End of picture text --> <!-- Start of picture text --> 40<br>‘A<br>20<br>2 ; apts Sa ae BS<br>2 0 Geee NY RS AS oe<br>Soe ae<br>-20 eden eae<br>Hj i0-20m te<br>a 20-40m aPe<br>Hi> 40m 7<br>-37<br>-20 0 20 40 54<br>longitude (°)<br><!-- End of picture text --> <!-- Start of picture text --> 40<br>= >» % ~ 4<br>PORES.<br>Y% »<br>Bae AN<br><ilm x :<br>29} MEi-10m 2<br>Mj i0-25m : j<br>M25Hi> som -50m —-wf!<br>-37<br>-20 0 20 40 54<br>longitude (°)<br><!-- End of picture text --> <!-- Start of picture text --> 40<br>=} corei 4<br>zz<br>x:<br>< 0.002 km?/yr<br>1) 0.002 - 0.02 km3/yr<br>-20 0.02 - 0.1 km3/yr i,. +<br>0.1- 0.3 km/yr a .<br>37 a > 0.3 km3/yr- Mad<br>-20 0 20 40 54<br>longitude (°)<br><!-- End of picture text -->
<!-- Start of picture text --> Sub-Saharan Africa GDEs by categories nN<br>(g) ©<br>Cabo hi Mauritania 2, . - 5 . : \<br> Verde ‘sg Mali 2 3 7 “ 4<br>a K nis ” Cha = 1 te \.<br>~~ Gambia rnee "NG scv tit Ge eo : © 48 8% 6 bag886 Djtoys<br>a Guinea Or ¥ Benin” - . “hy . a]<br>Sierra Leone“a Cote“ cvore Ghana Togo Nigerta .Pn4 “ wah Eth.—<br>GDE categories (Cat I) . a - oscc , Somaiia<br>af a<br>me | Inland surface waters Siateniendiacge .,' § os i<br>| Terrestrial springs any Boy ORE a ay<br>| Spring: a“ Burundi 2. te “3 A<br>= Coastal and marine ’ % ryAy4 t<br>a }| Terrestrial vegetation “Nc oh7 B ‘are" JA B) Malawi) feed<br>HM inland surface waters/ Coastal and Marine ay: ee ;<br>Terrestrial springs / Inland surface waters ae; KKSy . seats<br>HM _siinland surface waters/ Terrestrial vegetation ? Syiate\" a Madagascar %<br>tjadiba Botswana pe,<br>Administrative boundaries 7 WHOr op \<br>Studied countries re .<br>Countries with insufficient data 2. DP \gstho ,<br>Non-studied countries 5) On a<br>"a 0 500 1000km<br>Sources: Dataset from the SSA GDE inventory (Rambhunjun 2022), basemap from gadm 2022. Map created with OGIS and Inkscape. by Précila Rambhunjun. july 2022 | |<br><!-- End of picture text -->
6. _Aquifer transmissivity_ : for a given power, the greater the transmissivity, the higher the volume pumped by a water pumping system and thus the risk of over exploitation. Therefore, the lowest transmissivity value is allocated a 1 and the highest value a 5.

## **Classifying the datasets between each other’s**

The next step of the AHP is to classify the datasets based on their impact on the pumped volume (i.e. abstraction level) and thus on the risk of over exploitation. We choose to consider the annual average of GHI as the most important data as this study focuses on PVWPS and because GHI directly impacts the pumped volume (Meunier, 2019). Then, we consider the renewable groundwater resources as it provides information about the sustainably extractible resource. We consider that storage is coming next as it is the amount of groundwater that is still available in the event of over-abstraction of renewable resources. Then comes the population density as it significantly influences the water demand and thus has a potentially important impact on groundwater abstraction. Subsequently, we consider the static water level because it is directly linked to the resource accessibility. Finally, we consider the transmissivity, which is less directly linked to the pumped volume than the static water level. To assess the robustness of our choices, we compare the outcomes derived from these choices with the results obtained when assigning equal importance to each dataset (see Section 4).

## **Calculating the weights**

Following the AHP approach from (Saaty, 1977) and the classification detailed in the previous paragraph, the chosen pair wise comparison matrix is presented in Table 2. The consistency ratio for this pair wise comparison matrix is 0.027, which is acceptable (Saaty, 1977). The weights for each dataset drawn from this pair wise comparison matrix are summarized in Table 3.

||**Annual**<br>**average of GHI**|**Renewable groundwater**<br>**resources**|**Aquifer**<br>**storage**|**Population**<br>**density**|**Static**<br>**water level**|**Aquifer**<br>**transmissivity**|
|---|---|---|---|---|---|---|
|**Annual average of GHI**|1|2|3|4|5|6|
|**Renewable groundwater**<br>**resources**|0.5|1|2|3|4|5|
|**Aquifer storage**|0.33|0.5|1|2|3|4|
|**Population density**|0.25|0.33|0.5|1|2|3|
|**Static water level**|0.2|0.25|0.33|0.5|1|2|
|**Aquifer transmissivity**|0.16|0.2|0.25|0.33|0.5|1|

_Table 2 - Pair wise comparison matrix for the risk of over exploitation of groundwater resources._

|**Dataset**|**Weight**|
|---|---|
|Annual average of GHI|38 %|
|Renewable groundwater resources|25 %|
|Aquifer storage|16 %|
|Population density|10 %|
|Static water level|6.5 %|
|Aquifer transmissivity|4.5 %|

_Table 3 – Weight matrix for each dataset._

# 4. Results

The results using the weights of Table 3 are shown in Figure 2(a) and in Table 4. In Table 4, we classified the risk of over exploitation into 4 levels (the lower the level, the less risky). Results indicate that the risk of over exploitation is between 2 and 3 for 8% of the GDEs while 91% of them have a risk between 3 and 4. We see in Figure 2(a) that the major risk of over exploitation occurs in GDEs of western South Africa, Namibia, Kenya, Niger, and Somalia while the minor risk occurs in the GDEs of Congo, Gabon and southern Nigeria. This is due to the important difference in terms of annual average of GHI between these areas (see Figure 1(a)). Indeed, the annual average of GHI in western South Africa and Namibia is allocated a 4 while the one in Congo and Gabon is allocated ~1.75. This is also attributed to the significant difference in terms of renewable groundwater resources. Indeed, 6
<!-- Start of picture text --> ~ Sy<br>: e re<br>Riskier . j<br>P 7<br>Less risky ~*~ y<br><!-- End of picture text --> <!-- Start of picture text --> en ere ae Sn ee<br>y c = / WS qj See ve.<br>Riskier & :<br>i ee”<br>Less risky \ eEekReDy<br><!-- End of picture text -->
<!-- Start of picture text --> yal , | ce t<br>. ge ees on i aes<br>em fe R<br>Bent 2 4<br>Riskier >100 hab/25km? alt 7<br>Less 0 hab/25km? om fv<br>risky aes<br><!-- End of picture text -->

<!-- Start of picture text --> z 7 ri<br>Ss ite ae ‘ is al<br>oly Tita. *<br>Riskier >100 hab/25km?aa od,‘ £ 2 aneiy<br>Less 0 hab/25km? yelay<br>risky ep ae<br><!-- End of picture text -->
<!-- Start of picture text --> 100<br>8%<br>90 20<br>80 8%<br>60 43% 76%<br>Sis<br>40<br>21%<br>30<br>20<br>10 19%<br>0 And<br>os) os) <8) as)<br>wkGOP gO gO 5<br>a) @ volo wi<br>Nad ¥% 4* N h5<br><!-- End of picture text --> <!-- Start of picture text --> ae a | ae oh& Ra:we,<br>cash oe ue‘ x<br>Riskier 4<br>9 Shim,<br>r}<br>td AX<br>Less risky > =f<br><!-- End of picture text -->

<!-- Start of picture text --> 100<br>i. 90 25%<br>=Ne3Ne33 MA ; a8oor a8ooroor Aa}} =eReR : IN 0 49%As<br>Eee, iF<br>a fla fla AKG ay 60<br>ai Fie f= ; 26%<br>Riskier j hy44 6%<br>Less risky risky ee 10<br>0<br>e8) os) <8) as)<br>KgeGO ©]gO ooPggle<br>Nada) ¥% NJ 4” NJ» he5 K<br>a a L<br><!-- End of picture text --> <!-- Start of picture text --> i.<br>=Ne3Ne33 MA ; a8oor a8ooroor Aa}} =eReR : IN<br>Eee,<br>a fla fla AKG ay<br>ai Fie f= ;<br>Riskier j hy44<br>Less risky risky ee<br><!-- End of picture text -->
# 6. Policy implications

Irrigation has shaped civilizations across history and continues to present much potential in regions such as sub-Saharan Africa (SSA), where a small fraction of land is irrigated and even less by groundwater (Rodella, Zaveri and Bertone, 2023). Irrigation can significantly increase production, especially in arid and semi-arid regions (Kukal and Irmak, 2019, Fernández-Cirelli et al., 2009). In the case of SSA, shallow groundwater irrigation has the potential to be game-changing, protecting farmers from weather shocks and helping countries of the region tackle food insecurity (Gowing et al., 2016; Rodella, Zaveri and Bertone, 2023).

With stunting affecting one in four children in the SSA region, the question is not whether to expend groundwater irrigation, knowing that access to shallow groundwater can decrease the chances of childhood stunting by 20% for rural children in this region by protecting agricultural productivity (Rodella, Zaveri and Bertone, 2023), but how to do so sustainably, minimizing unintended consequences (Balasubramanya et al., 2024). Lessons from other regions, such as South Asia and the Middle East, can guide these efforts.

The results presented in our paper provide novel insights into some of those risks as they relate to groundwater-dependent ecosystems. They are threatening GDEs and present three main issues. First, as GDEs are poorly mapped or monitored, their total value and benefits need to be better understood and measured. Yet, with slight variation in groundwater level needed, there is little chance of restoration when they are gone due to their fragile nature, particularly in dryland areas (Rohde et al., 2017). Second, GDEs are important for the livelihoods of populations in rural areas that are typically more vulnerable. An unfettered provision of solar pumping could lead to a deterioration of GDEs on which pastoralists rely for their cattle while also expanding agricultural land to areas previously used for transhumance and grazing, heightening tensions between farmers and pastoralists (Rodella, Zaveri and Bertone, 2023). Third, beyond their importance for wildlife – including for migratory birds – GDEs play an essential role in carbon storage (Mendonça et al. 2017). Countries seeking to reduce their emission by switching groundwater pumping to solar, owe to consider the carbon impacts of compromising the role GDEs play as carbon sink.

For those reasons, the results highlight the necessity for policymakers and development partners to collaborate upstream on largescale solar energy deployment in regions with high irrigation potential, such as SSA, that will facilitate easier and cheaper access to much-needed solar pumping irrigation but require enforceable policy and regulation to protect against unintended consequences, such as the deterioration or destruction of GDEs. Our analysis also highlights the need for more data on GDEs from location to the services they provide to people and the environment to monitor better their health and address situations of poor groundwater management that could threaten their existence. The proper monitoring of GDEs can thus be an efficient strategy to contribute early warning information on the mismanagement of groundwater resource and help prevent or remedy impacts.

# 7. Conclusion

We proposed an analytical hierarchy process to evaluate the risk posed to groundwater dependent ecosystems (GDEs) by an uncontrolled expansion of access to groundwater through photovoltaic pumping in sub-Saharan Africa. More specifically, we evaluated the risk of over exploitation of groundwater resources which could endanger GDEs, and we considered the following input data: global horizontal irradiance, renewable groundwater resources, groundwater storage, population density, static water level and aquifer transmissivity. We found that numerous GDEs in southern and eastern Africa have a higher risk of over exploitation, especially in South Africa and Namibia. On the opposite, we found that GDEs in the regions of Gabon, Congo and southern Nigeria are less at risk. Additionally, by comparing our results with the number of people relying on an unimproved water source in 2017, we highlighted regions like southern Nigeria and South Sudan that could be prioritized for investments in new photovoltaic water pumping systems (PVWPS) because of the higher groundwater development need and the lower risk posed by photovoltaic pumping to GDEs. On the opposite, in other regions, like in Namibia and South Africa, where the groundwater development need is lower while the risk posed by PVWPS to GDEs is higher, investments should be wisely targeted, and a very close monitoring of groundwater resources will be required.

Despite the limitations (see Section 5), the results of this study are important in highlighting some of the unintended consequences that could result from a scaling up of photovoltaic pumping without the adequate safeguards in place to assess the potential impacts on GDEs. The findings can help policymakers and implementing ministries and agencies integrate in their development planning the potential areas where the development of PVWPS could be prioritized and where it must be more carefully monitored to ensure a sustainable use of the groundwater resources and a reduced impact on GDEs.

10
# 8. References

Balasubramanya, S., Garrick, D., Brozović, N., Ringler, C., Zaveri, E., Rodella, A.-S., Buisson, M.-C., Schmitter, P., Durga, N., Kishore, A., 2024. Risks from solar-powered groundwater irrigation. Science 383, 256–258.

Barron, O.V., Emelyanova, I., Van Niel, T.G., Pollock, D., Hodgson, G., 2014. Mapping groundwater-dependent ecosystems using remote sensing measures of vegetation and moisture dynamics. Hydrol. Process. 28, 372–385. https://doi.org/10.1002/hyp.9609.

- Bonsor, H.C., MacDonald, A.M., 2011. An initial estimate of depth to groundwater across Africa. British Geological Survey Open Report. https://nora.nerc.ac.uk/id/eprint/17907/1/OR11067.pdf. Accessed 15 Dec 2022.

- Center for International Earth Science Information Network, 2018. Gridded Population of the World. https://sedac.ciesin.columbia.edu/data/set/gpw-v4-population-density-rev11. Accessed 22 Apr 2023.

- Chandel, S.S., Nagaraju Naik, M., Chandel, R., 2015. Review of solar photovoltaic water pumping system technology for irrigation and community drinking water supplies. Renew. Sustain. Energy Rev. 49, 1084–1099. https://doi.org/10.1016/j.rser.2015.04.083.

- Esteban, E., Dinar, A., 2016. The Role of Groundwater-Dependent Ecosystems in Groundwater Management. Nat. Resour. Model. 29, 98–129. https://doi.org/10.1111/nrm.12082.

- European Commission, 2021. Copernicus Atmosphere Monitoring Service (CAMS). http://www.soda-pro.com/web-services/radiation/camsradiation-service. Accessed 15 Dec 2022.

Fan, Y., Li, H., Miguez-Macho, G., 2013. Global patterns of groundwater table depth. Science 339, 940–943.

- Fernández-Cirelli, A., Arumí, J. L., Rivera, D., Boochs, P. W., 2009. Environmental effects of irrigation in arid and semi-arid regions. Chilean Journal of Agricultural Research 69, 27-40.

- Gebrezgabher, S., Leh, M., Merrey, D.J., Kodua, T.T., Schmitter, P., 2021. Solar photovoltaic technology for small-scale irrigation in Ghana: suitability mapping and business models. Agricultural Water Management – Making a Business Case for Smallholders. International Water Management Institute (IWMI). https://doi.org/10.5337/2021.209.

- Global Solar Atlas, 2024. Global Photovoltaic Power Potential by Country. https://globalsolaratlas.info/global-pv-potential-study. Accessed 06 Sept 2024.

- Gowing, J., Parkin, G., Forsythe, N., Walker, D., Haile, A. T., Alamirew, D., 2016. Shallow groundwater in sub-Saharan Africa: neglected opportunity for sustainable intensification of small-scale agriculture? Hydrology and Earth System Sciences Discussions, 2016, 1-33.

- Huang, Z., Hejazi, M., Li, X., Tang, Q., Vernon, C., Leng, G., Liu, Y., Döll, P., Eisner, S., Gerten, D., Hanasaki, N., Wada, Y., 2018. Reconstruction of global gridded monthly sectoral water withdrawals for 1971–2010 and analysis of their spatiotemporal patterns. Hydrol. Earth Syst. Sci. 22, 2117–2133. https://doi.org/10.5194/hess-22-2117-2018.

- IEA, IRENA, UNSD, World Bank, WHO. 2024. Tracking SDG 7: The Energy Progress Report. World Bank, Washington DC. World Bank. https://trackingsdg7.esmap.org/data/files/download-documents/sdg7-report2024-0611-v9-highresforweb.pdf. Accessed 06 Sept 2024.

- Institute for Health Metrics and Evaluation (IHME), 2020. LMIC Drinking Water and Sanitation Access Geospatial Estimates 2000-2017. https://cloud.ihme.washington.edu/s/bkH2X2tFQMejMxy?path=%2F. Accessed 15 Dec 2022.

- Khan, A. M., & Rodella, A. S., 2021. A Hard Rain's a-Gonna Fall?: New Insights on Water Security and Fragility in the Sahel. The World Bank. https://documents.worldbank.org/en/publication/documents-reports/documentdetail/693481634066645154/a-hard-rains-a-gonna-fallnew-insights-on-water-security-and-fragility-in-the-sahel. Accessed 06 Sept 2024.

- Kukal, M. S., & Irmak, S., 2019. Irrigation-limited yield gaps: trends and variability in the United States post-1950. Environmental Research Communications, 1(6), 061005.

- Lezzaik, K., Milewski, A., Mullen, J., 2018. The groundwater risk index: Development and application in the Middle East and North Africa region. Sci. Total Environ. 628, 1149–1164.

- MacDonald, A. M., Bonsor, H. C., Dochartaigh, B. É. Ó., Taylor, R. G., 2012. Quantitative maps of groundwater resources in Africa. Environmental Research Letters, 7(2), 024009.

- McCallum, A. M., Andersen, M. S., Giambastiani, B. M., Kelly, B. F., Ian Acworth, R., 2013. River–aquifer interactions in a semi‐arid environment stressed by groundwater abstraction. Hydrological Processes, 27(7), 1072-1085.

- Mendonça, R., Müller, R. A., Clow, D., Verpoorter, C., Raymond, P., Tranvik, L. J., Sobek, S., 2017. Organic carbon burial in global lakes and reservoirs. Nature communications, 8(1), 1694.

- Meunier, S., 2019. Optimal design of photovoltaic water pumping systems for rural communities – a technical, economic and social approach. Doctoral dissertation. Université Paris-Saclay.

- Meunier, S., Heinrich, M., Quéval, L., Cherni, J.A., Vido, L., Darga, A., Dessante, P., Multon, B., Kitanidis, P.K., Marchand, C., 2019. A validated model of a photovoltaic water pumping system for off-grid rural communities. Appl. Energy 241, 580–591. https://doi.org/10.1016/j.apenergy.2019.03.035.

Mukherjee, A., 2018. Overview of the groundwater of South Asia. Springer.

- Murray, B.B.R., Zeppel, M.J.B., Hose, G.C., Eamus, D., 2003. Groundwater‐dependent ecosystems in Australia: It’s more than just water for rivers. Ecol. Manag. Restor. 4, 110–113. https://doi.org/10.1046/j.1442-8903.2003.00144.x.

- Murray, B.R., Hose, G.C., Eamus, D., Licari, D., 2006. Valuation of groundwater-dependent ecosystems: a functional methodology incorporating ecosystem services. Aust. J. Bot. 54, 221–229. https://doi.org/10.1071/BT05018.

11
Ozano, K., Roby, A., MacDonald, A., Upton, K., Hepworth, N., Gorman, C., Matthews, J.H., Dominique, K., Trabacchi, C., Chijiutomi, C., Tshabalala, Z., Joshi, D., Udalagama, U., Nicol, A., 2022. Groundwater: Making the Invisible Visible: FCDO Briefing Pack on Water Governance, Finance and Climate Change. Report. https://nora.nerc.ac.uk/id/eprint/532312/. Accessed 25 Mar 2023.

- Rodella, A. S., Zaveri, E., Bertone, F., 2023. The Hidden Wealth of Nations: The Economics of Groundwater in Times of Climate Change. Washington, DC: World Bank. https://openknowledge.worldbank.org/server/api/core/bitstreams/5f1877a1-b30f-42c3-8fe29bdd581d915c/content. Accessed 23 Dec 2023.

- Rohde, M.M., Albano, C.M., Huggins, X., Klausmeyer, K.R., Morton, C., Sharman, A., Zaveri, E., Saito, L., Freed, Z., Howard, J.K., Job, N., Richter, H., Toderich, K., Rodella, A.-S., Gleeson, T., Huntington, J., Chandanpurkar, H.A., Purdy, A.J., Famiglietti, J.S., Singer, M.B., Roberts, D.A., Caylor, K., Stella, J.C., 2024. Groundwater-dependent ecosystem map exposes global dryland protection needs. Nature 632, 101–107. https://doi.org/10.1038/s41586-024-07702-8.

- Rohde, M. M., Froend, R., Howard, J., 2017. A global synthesis of managing groundwater dependent ecosystems under sustainable groundwater policy. Groundwater, 55(3), 293-301.

- Saaty, T.L., 1977. A scaling method for priorities in hierarchical structures. J. Math. Psychol. 15, 234–281. https://doi.org/10.1016/00222496(77)90033-5.

- Schmitter, P., Kibret, K.S., Lefore, N., Barron, J., 2018. Suitability mapping framework for solar photovoltaic pumps for smallholder farmers in sub-Saharan Africa. Appl. Geogr. 94, 41–57. https://doi.org/10.1016/j.apgeog.2018.02.008.

- Soenen, C., Reinbold, V., Meunier, S., Cherni, J.A., Darga, A., Dessante, P., Quéval, L., 2021. Comparison of Tank and Battery Storages for Photovoltaic Water Pumping. Energies 14, 2483. https://doi.org/10.3390/en14092483.

- Taylor, C. J., Alley, W. M., 2001. Ground-water-level monitoring and the importance of long-term water-level data. US Geological Survey. https://pubs.usgs.gov/circ/circ1217/pdf/circ1217_final.pdf. Accessed 15 Dec 2022.

- UNICEF, WHO, 2022. Progress on drinking water, sanitation and hygiene in Africa 2000-2020: Five years into SDGs. https://www.unicef.org/wca/reports/progress-drinking-water-sanitation-and-hygiene-africa-2000-2020. Accessed 06 Sept 2024.

- Vezin, T., Meunier, S., Quéval, L., Cherni, J.A., Vido, L., Darga, A., Dessante, P., Kitanidis, P.K., Marchand, C., 2020. Borehole water level model for photovoltaic water pumping systems. Appl. Energy 258, 114080. https://doi.org/10.1016/j.apenergy.2019.114080.

- Wada, Y., Van Beek, L.P., Van Kempen, C.M., Reckman, J.W., Vasak, S., Bierkens, M.F., 2010. Global depletion of groundwater resources. Geophys. Res. Lett. 37.

- Xie, H., Ringler, C., Mondal, Md.A.H., 2021. Solar or Diesel: A Comparison of Costs for Groundwater-Fed Irrigation in Sub-Saharan Africa Under Two Energy Solutions. Earths Future 9, e2020EF001611. https://doi.org/10.1029/2020EF001611.

12