Crop yields response to water pressures in the Ebro basin in Spain: risk and water policy implications

Abstract

Abstract. The increasing pressure on water systems in the Mediterranean enhances existing water conflicts and threatens water supply for agriculture. In this context, one of the main priorities for agricultural research and public policy is the adaptation of crop yields to water pressures. This paper focuses on the evaluation of hydrological risk and water policy implications for food production. Our methodological approach includes four steps. For the first step, we estimate the impacts of rainfall and irrigation water on crop yields. However, this study is not limited to general crop production functions since it also considers the linkages between those economic and biophysical aspects which may have an important effect on crop productivity. We use statistical models of yield response to address how hydrological variables affect the yield of the main Mediterranean crops in the Ebro river basin. In the second step, this study takes into consideration the effects of those interactions and analyzes gross value added sensitivity to crop production changes. We then use Montecarlo simulations to characterize crop yield risk to water variability. Finally we evaluate some policy scenarios with irrigated area adjustments that could cope in a context of increased water scarcity. A substantial decrease in irrigated land, of up to 30% of total, results in only moderate losses of crop productivity. The response is crop and region specific and may serve to prioritise adaptation strategies.

Do Water Rights Affect Technical Efficiency and Social Disparities of Crop Production in the Mediterranean? The Spanish Ebro Basin Evidence

“…We can see that in general the impact of these changes on social distribution of incomes is more significant in the areas where the cereals are dominant, and particularly the major impacts on technical efficiency are produced for barley and alfalfa crops. According to the results in the previous section, policies of reducing area under irrigation can be a non-dramatic solution for production [8,11,12], but in the long term they negatively affect the competitiveness and increasing social inequality in agriculture. Figure 6 shows the marginal effect of the irrigated area on competitiveness and income distribution looking at province level and taking into account the agricultural gross value added.…”

“…Table 3 shows the estimated crop production functions for the five crops in the study. We selected the Cobb-Douglas production function form for all studied crops, first, due to its simplicity and validity [30] and its acceptance in the literature of production functions in agricultural economics [8,43,44] and second, due to the inherent problem of collinearity presented by the translog functions. Specifically, when we estimate the translog specification, we observe highly correlation between the new explanatory variables, high variance inflation factor and severe problems for the condition numbers (taking into account the guidelines reported in [45]), then we choose to try with a different specification of the model (Cobb-Douglas) using the same data and it produces shifts suggesting weak collinearity problems.…”

“…We can observe that the coefficient for ln(irrig) in grapevine is negative what is due to the fact that grapevine is a rain fed crop and in this area include very high quality production (La Rioja, Rivera del Duero, Penedes, Navarra DO, etc.) where only deficit irrigation is being applied to maintain yield during drought periods ( [8]) since exceed water can affect the wines quality. Therefore, when scarcity problems arise, the water for irrigation is increased to maintain the crop, but still worse outputs can be expected due to the drought effects.…”

“…accomplish the legal requirements of the WFD [8,14] and we focus on the analysis of water demand reduction for agricultural use through decreasing on irrigated areas.…”

Parameter optimisation for a better representation of drought by LSMs: inverse modelling vs. sequential data assimilation

“…In the context of climate change and of natural climate variability, there is a need to monitor the impacts of droughts on crops and water resources at continental and global scales (Quiroga et al, 2011;Van der Velde et al, 2012;Crow et al, 2012;Bastos et al, 2014). Modelling of continental surfaces into atmospheric and hydrological models has evolved in recent decades towards land surface models (LSMs) able to simulate the coupling of the water, energy and carbon cycles (Calvet et al, 1998;Krinner et al, 2005;Gibelin et al, 2006).…”