These point estimates are converted to gridded estimates at a spatial resolution of 0.1 x 0.1 degrees (approximately 10km x 10km) for the purposes of calculation. The software also provides an option to use NMA station data modified with satellite data on cloud cover to improve the grid of estimated precipitation<sup>9</sup> .

**<mark>Box 2.1: WFP LEAP calculation of yield shortfall</mark>**

<mark>LEAP calculates yield shortfall by combining a model for water balance (the FAO’s Water Requirement Satisfaction Index (WRSI)) with a model describing crop yield response to water stress (Doorenbos and Kassam, 1979):</mark> <mark>100‐((1‐(1‐A/B)*K</mark> y <mark>)*100)</mark> <mark>Where:</mark> <mark>‐ A is the</mark> **<mark>Actual Evapotranspiration</mark>** <mark>;</mark>

- <mark>B is the</mark> **<mark>Total Water Requirement without water stress</mark>** <mark>; and</mark>

<mark>‐ K</mark> y <mark>is a crop specific factor – “</mark> **<mark>Yield Response Factor</mark>** <mark>” ‐ for growing seasons or stages of growing seasons,</mark> derived empirically from actual measured crop yield responses to water under good growing conditions<sup>10</sup> . <mark>The WRSI gives the ratio of</mark> **<mark>Actual Evapotranspiration</mark>** <mark>to</mark> **<mark>Total Water Requirement</mark>** <mark>(i.e. A/B in the above) for a season. ‐ The</mark> **<mark>Actual Evapotranspiration</mark>** <mark>represents the actual amount of water withdrawn from the soil water reservoir and is calculated indirectly using rainfall data within a model of soil water balance. It requires inputs of time‐variable rainfall data and soil and crop‐specific data (soil water holding capacity and crop‐ specific maximum allowable water depletion);</mark> <mark>‐ The</mark> **<mark>Total Water Requirement</mark>** <mark>is calculated as (Potential Evapotranspiration x Crop Coefficient). It requires empirically‐derived crop coefficients to relate the reference evapotranspiration to the relevant crop, and time‐variable climate data inputs of;</mark> <mark>`o` Solar radiation (sunshine);</mark> <mark>`o` Air temperature;</mark> <mark>`o` Humidity; and</mark> `o` Wind speed.

<mark>The reference evapotranspiration expresses the evaporating power of the atmosphere at a specific location and time of the year. Both average and recorded values are suitable for use in the methodology described above, with recorded (actual) values preferred.</mark> <mark>Sources: (Heofsloot & Calmanti, 2012), (Frère, M, and Popov, G, 1979), (Frère, M, and Popov, G, 1986), (Abraha, M, 2013),</mark> <u><mark>(Doorenbos, J. & Kassam, A, 1979).</mark></u> The LEAP protocol for assessing crop yield loss estimates only meteorological drought arising from rainfall variability. This has been criticized as limiting the extent to which the LEAP crop loss figures capture experience on the ground, as they do not capture the many other factors (such as pests) impacting yields<sup>11</sup> . It is worth reiterating here that the purpose of this paper is not to derive relationships between household poverty and crop yield losses. Rather, the purpose is to establish the validity of relationships derived between a selected poverty indicator and a measure of natural hazard that could be modelled within established probabilistic catastrophe risk modelling frameworks. We are interested in the covariate shocks that can arise from rainfall variability, as this

> 9 http://www.hoefsloot.com/Downloads/The%20SEDI%20interpolation%20method%20.pdf 10 Doorenbos and Kassam, 1979

> 11 As demonstrated by a 2007 ground‐truthing exercise described in: FSCB/WFP Workshop Livelihood Early Assessment and Protection (LEAP): its potential application, benefits and limits, NOTE FOR THE RECORD. 21<sup>st</sup> January 2008.

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