Reallocating regional water apparent productivity in the long term: methodological contributions and application for Spain

The main objective of this paper is to quantify and explain the main trends and determinants of long-term agricultural water apparent productivity (WAP). The WAP shows the economic value of products per cubic meter of water used and is calculated as the ratio between the value of agricultural production and its water use (the water footprint). In order to understand economic and agricultural structural changes, we use index decomposition analysis, novel in the study of WAP. This approach is consistently multidimensional (results for different crops and provinces are analyzed) and multilevel (different levels of crops and regional disaggregation are combined), and hence applications are possible for different regions and settings. In the case of Spanish agriculture (analyzed here), the study is of particular importance, given the profound political, economic, and agricultural transformations experienced in the twentieth century. Furthermore, given Spain's particular environmental conditionssuch as the high number of sunshine hours and the unequal distribution of rainfallthe spatial and temporal differences are notable in terms of crop production composition, economic value, and water footprint. The results show a 27% increase in agricultural WAP from 1955 to 2005-2010, totally explained by an improvement in water efficiency (intensity effect reflecting the use of water relative to the production attained) that happened in most areas of the country. The relative variations in the regional composition of the water footprint (share effect), and especially the crop production patterns (composition effect), contributed to a slowdown in total WAP at the country level. However, the share and composition effects encouraged the WAP's growth in South and Southeast Spain, areas that produced high value-added crops with large water needs.