In arid and semi-arid Mediterranean basins maintaining a long term balance of water resources is a crucial point given the high variability of rainfall and the intense exploitation of water. The impact of historical land cover changes witnessed in Mediterranean regions during the last two decades on the hydrologic response of their corresponding river basins is an issue of paramount importance that has received little attention so far and may have significantly altered the water balance. This hypothesis has been tested for the case of the Mar Menor catchment in the Segura River Basin in Spain.
GIS based models are normally implemented to assess the effect of Land Use and Land Use Change (LULUC) over runoff dynamics. This approach is frequent to estimate runoff generation during single rainfall events. Following such principles Pérez Blanco, Viavattene and Gómez Gómez expand this methodology and assesse the probability of every rainfall event and thus of every runoff scenario in order to obtain expected or long term average annual runoff (see attached document). Combining this value with several evapotranspiration (ET) methods, expected groundwater recharge is calculated. In all this process geomatics plays a key role providing the necessary tools to solve the most computationally demanding parts of the methodology.
The model is built over rainfall data. The intensity and distribution of rainfall events are the inputs of the system, while the hydromorphological characteristics of the basin, land use, slope and humidity antecedents regulate the generation of runoff for a certain rainfall event. All these values are obtained for every single raster in the catchment model. Rainfall event data series is adjusted to a Gamma function so the event distribution is smoothed and closer to real rainfall dynamics. There are basically an infinite number of likely rainfall events and the runoff simulation has to be carried out for every one of them. We combine Matlab with GIS data series in order to allocate a runoff value for every raster in the basin model. Then expected runoff is obtained, and from here and expected ET values, expected groundwater is estimated.
The results obtained with this methodology support the role of LULUC as a relevant factor explaining water balance dynamics. LULUC experienced in Mediterranean basins has resulted in higher expected runoff and reduced groundwater recharge rates. This may result in more frequent flood events and, perhaps more importantly, it is likely to put more pressure over overexploited groundwater resources and worsen the structural scarcity as well as increase drought frequency in Mediterranean areas such as the Mar Menor catchment.
The work can be found in our Cuadernos de Geomática Aplicada section.
The work can be found in our Cuadernos de Geomática Aplicada section.
