Application of satellite data for the quantification of agricultural water use in the context of the transboundary water system of Titicaca Lake, Desaguadero River, and Poopo Lake in South America
Authors: Ayala Ticona Gustavo , Santos Tania , Gonzales Camilo , Purkey David 
Published: March 2024

In the context of transboundary water systems, one of the most relevant challenges involves the quantification of water use for large scale activities such as agriculture. Whether due to methodological differences in the consolidation of inventories of agricultural areas, their production calendars, or due to differences in data availability between neighboring countries, the consolidation of detailed information of water use represent a process to be improved for an appropriate allocation of resources in transboundary management. On the other hand, the advantages in the availability and spatiotemporal homogeneity of satellite data, added to the connotation to minimize issues related to neutrality and stakeholder biases involving the use of only local data threatening consensus in a transboundary framework, offers a strategical opportunity to enhance the integrated water management by using satellite data.Under these considerations, the present study applies Landsat satellite images for the spatial and temporal quantification of agricultural water use in the transboundary region (110 969 km2) of the Titicaca Lake, Desaguadero River, and Poopo Lake System (TDP) located between Bolivia (55%), Chile (1%), and Peru (44%) in South America (Lima-Quispe et al., 2022). Data processing first allows, to define irrigated agricultural areas from those which are not irrigated, through a validation process using the inventory of agricultural areas available in the official repositories of the countries and running an analysis using climate data (precipitation and potential evapotranspiration), second; defines the spatiotemporal pattern of water use through the evaluation and combination of vegetation indices (NDVI, EVI, among others) for the total agricultural area of the TDP water system (Linear Regressions) for the crops with the largest extension and/or use of water (potatoes, bean, quinoa, barley) studied at the local level in a process of calibration and validation (Bretreger et al., 2019). The results, from the analysis make possible to classify divergences attributed to the methodology, and use of the remote sensing data (correlation, BIAS in relation to local data) as well as to identify areas where both at the level of surface extension and temporal pattern, real water use would be exceeding the permitted and feasible values (trend test analysis) and therefore would imply a critical condition of alteration over the water bodies involved, which stakeholders may pay attention whether through increasing monitoring to corroborate or to strength penalties for ecosystem protection.References:Lima-Quispe, N., Escobar, M., Wickel, A. J., von Kaenel, M., &amp; Purkey, D. (2021). Untangling the effects of climate variability and irrigation management on water levels in Lakes Titicaca and Poop&#243;. Journal of Hydrology: Regional Studies, 37, 100927.Bretreger, D., Yeo, I. Y., Quijano, J., Awad, J., Hancock, G., &amp; Willgoose, G. (2019). Monitoring irrigation water use over paddock scales using climate data and landsat observations. Agricultural water management, 221, 175-191.