Drought Monitoring Systems
Drought monitoring systems are key to tracking and mapping drought spatial extent and intensity throughout time, establishing links between drought status and adequate actions to be taken, and analyzing the effectiveness of the measures implemented.
Spain has a countrywide drought monitoring system managed by the Ministry for Agriculture, Food and the Environment (MAGRAMA). This system is based on information from several hydrological variables, such as reservoir storage, groundwater piezometric levels, streamflow, reservoir inflows, and precipitation. These variables are measured at several locations throughout the river basins and are weighted to obtain an integrated indicator, or a concept definition specific to Spain, on the basis of a national indicator system (Estrela and Vargas 2012). That indicator (Indice de Estado—Index of Status) is meant to represent the hydrological status in each river basin. For example, if the water uses of a region depend on the water stored in a reservoir, the drought index is based on the reservoir level; if water uses depend on groundwater, the piezometric levels of the aquifer are the data used to calculate the index. The index is obtained according to the percentiles of each key variable for each hydrological system. The values obtained for the current situation are compared to the drought thresholds, resulting in the establishment of a corresponding drought alert level. The standardized values of the indicators (ranging from 0 to 1) provide the basin drought status levels, classified as normal, prealert, alert, and emergency. A normal situation corresponds to a hydrological condition better than the average conditions, defined by historical evaluation. The other drought status levels (prealert, alert, and emergency) correspond to hydrological conditions with values below the average (CHG 2007).
Each of the drought alert levels is associated with specific management actions, which are specified in the DMPs, developed for each RBD. For example, in a prealert situation, the RBA encourages farmers to revise their cropping plans to consider the available water resources (Estrela and Vargas 2012; Stefano et al. 2015).
The RBDAs periodically send follow-up information to the Water Directorate of MAGRAMA, which compiles the data from every RBDA to produce a common dataset and reports on drought information, conditions, and measures in the Spanish territory. This information (with maps, graphs, and statistics) is presented by the National Drought Observatory, for the entire Spanish territory, usually on a monthly basis (MAPAMA 2016b) (Figure 23.4).
Spatial distribution of the hydrological status index in June 2012, corresponding with the last severe drought episode that affected the IP
In parallel, there is some available information on real-time drought conditions in Spain. The Spanish State Meteorological Agency, AEMET, produces national maps of the monthly information about meteorological drought status using the SPI. This index is calculated based on precipitation records (AEMET 2016).
Agricultural drought monitoring in Spain follows two approaches. The first approach involves a drought monitoring system for pasturelands based on anomalies recorded from the time series of MODIS images (http://www. mapama.gob.es/es/enesa/lineas_de_seguros/seguros_ganaderos/per- dida_pastos.asp). According to the vegetation indices calculated from these images, a threshold is fixed to determine if pasturelands of each region show a significant decrease of leaf production and net primary production associated with drought. Hence, based on the remote sensing system, and in accordance with the evolution of expected losses in productivity, economic compensation is given to the farmers that have pasture insurance. The second approach is based on agricultural monitoring developed by the national company for agricultural insurance (AGROSEGURO, http:// agroseguro.es/). High spatial density field surveys are carried out to determine crop conditions in the different phenological stages. If crop failure is declared in an area, an evaluation is done to determine the expected losses in each agricultural use and the corresponding insurance compensation to the farmers.