Aplicación de teledetección y gestión integrada del agua en zonas semiáridas

Abstract

ABSTRACT Water is an essential resource for the maintenance of natural ecosystems, climate regulation and the development of humanity. The growing pressure on this resource in recent decades and changes in the climate make a priority to evaluate and protect our natural resources in a cooperative manner, towards the same objectives. Therefore, legislation and the administration management are essential to carry out different strategies to implement projects that favor the coordinated, equitable and sustainable use of water resources and achieve the objectives of hydrological planning. Some of the plans proposed by the administrations consist of monitoring the quantitative and qualitative status of both groundwater and surface water, adaptation measures and mitigation of the effects of climate change, recovery of river ecosystems and improvements in their ecological status, adaptations and management of flood risks, plans to minimize the effects of drought situations, safety management of dams and reservoirs, as well as new proposals and measures to promote the purification, sanitation and reuse of water. With these strategies, it is intended to develop a methodology that allows achieving the fulfillment of the social, environmental and economic objectives set out by the community and national management policies. Beside these strategies, desalination is one of the major targets of the administration. On this basis, the purpose of this thesis is to highlight the capacity of remote sensing and Geographic Information Systems (GIS) in hydrological planning, not only as a tool for diagnosing the current state of resources but also to incorporate it into the decisionmaking process. Remote sensing provides us with a large amount of complementary information to that obtained in situ, to which, in addition, other types of environmental parameters can be included as indicators of the effects produced by climate change. In the articles that comprise this thesis, an evaluation of water resources was carried out based on simple methodologies with satellite images and the formulation of models that allow predicting the availability of water under various scenarios of water scarcity. At the same time, one of the strategies for reuse and obtaining resources such as desalination is added. To evaluate the changes in land use and its relationship with water consumption, an analysis was carried out using aerial images at a hydrographic basin scale, in an area that, despite being affected by arid conditions, has produced a large population growth and intensification of agricultural activity. In the first publication, "Water Management in Irrigation Systems by Using Satellite Information", water losses due to evaporation were estimated in relation to with the increase in the number of ponds for irrigation comparing two study periods, between 1973-1986 and in 2016. In this study period, an increase by four in the number of ponds has been estimated, which means an increase in losses by annual evaporation of around 15.62 hm³/year. The use of satellite images and the calculation of spectral indices to obtain information on the evolution, state and availability of water resources has become in recent years a common tool mainly for the agricultural sector and the study of natural ecosystems. In the second publication, "A review of Landsat TM/ETM based vegetation indices as applied to wetland ecosystems", information from Landsat 5 of the area located between the Salinas de Santa Pola and the Natural Park of El Hondo in Elche and Crevillente was used, with the aim of evaluate the fit of various vegetation indices in wetland areas. A direct relationship and a high correlation were found between biomass estimation indices. On the other hand, for the moisture content indices, they did not indicate a good correlation. These results show that the selection of the different indices must be made according to the characteristics of the area, considering that, for example, in areas with low plant density and greater exposure, those that correct the distortions produced by ground reflectivity should be chosen. In the case of the third publication, “Assessing water availability in Mediterranean regions affected by water conflicts through MODIS data time series analysis”, time series of MODIS images from 2001 to 2014 of the Normalized Difference Index (NDVI) and Land Surface Temperature (LST) located in the hydrographic basins of the Amadorio and Guadalest rivers. Daily precipitation data, annual volume stored in both reservoirs, and climate model projections for 2050 were also used. With the calculation of the anomalies of this data series, it was possible to visualize spatio-temporal patterns of change in order to analyze the relationship between the volume of water stored in the reservoirs and the rest of the variables (NDVI, LST and precipitation), finding a significant correlation between the NDVI and the data on the volume of water stored. In addition, the prediction capacity of water storage, NDVI and LST was evaluated considering climate change scenarios, in which a significant inverse relationship with LST is shown. The objective of the fourth publication, “Using Landsat images to determine water storing capacity in Mediterranean environments”, was to estimate and model the water storage capacity with the possibility of incorporating it into an automated control and management system. To do this, the supervised classification of a time series of Landsat images was used to extract an estimate of the surface of the water table and generate prediction models. In the validation, values were obtained that indicated a good fit and a good predictive capacity. For sustainable resources management it is necessary to implement methods that guarantee the maximum water exploitation while reducing the current pressure. One of the proposals that defines national and community policies is water reuse and depuration as a key strategy in achieving the objectives. In the fifth publication, “Agricultural drainage water characterization to determine the desalination possibilities for irrigation in a semiarid environment”, the quality of agricultural drainage water was evaluated to determine the possibility of implementing a desalination system for its reuse as unconventional water resources. Flow rate, pH, electrical conductivity, chloride and sodium, and total dissolved solids were analyzed in different samplings. Although in some of drainage canals a highly variable flow and high salinity and dissolved solids values were obtained, in other cases, data indicated the possibility of installing a small reverse osmosis plant for the desalination and reuse of water. In conclusion, water must be treated with an overall vision, integrated management, so that the resources and their collection are under a control system in which remote sensing offers a series of possibilities and would be combined with other strategies and processes. Without any doubt, and focusing on the immediate environment, the scarcity of resources calls for the need to reuse water as much as possible, including surplus water, and desalination, not only of seawater, many possibilities existing, as has been shown.