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ESTIMATION OF THE IMPACT OF CLIMATE AND LAND USE CHANGES ON THE AVAILABILITY OF WATER RESOURCES AND DROUGHT RISK

Irena Yordanova

Abstract

Climate change exerts influence on water resources and runoff directly ? by altering natural factors (precipitation, temperature, evapotranspiration) and indirectly ? by induced as a result of climate change land use alterations (forests, wetlands, etc.). The report presents the methodological approach for estimation of the cumulative impact of both climate and land use changes on the availability of water resources. For calculation of water balance a Model of monthly water balance, created in the United States Geological Survey, is used. The model is based on the Thornthwaite methodology. A methodology for analysis, caused by forest ecosystem changes of the input parameters of the water balance model, has been developed. The results, determining the ecological conditions in forest ecosystems, are taken into consideration. The factors related to land cover changes are: the retention capacity of the terrain, the moisture capturing capacity of the active soil layer, depending on the mechanical composition of the soils and the root system, the respective change of the direct runoff, the rate of snow thawing, etc.. To assess the impact of land use changes on the runoff, the water balance model is applied, as well as the SCS curve method, which operates with the so-called hydrologic soil-vegetation groups. SCS method is used to estimate the direct runoff and for taking into account the influence of changes in forest ecosystem, due to climate variability. A methodology for minimum ecological flow assessment is included also. The threshold level method is used to determine the drought periods, considered like critical periods in relation with the water demand. In order to evaluate the available resource and drought risk assessment, it were determined the long-term average discharge, the deficiency depth and low flow periods frequency. The drought frequency and severity at present, the different climatic and land use scenarios are analysed. The results from international projects and application in practice are presented. The developed methodology is related to the River Basin Management Plans, Drought risk assessment and adaptive management under condition of climate changes for the purposes of Water Framework Directive (WFD) and Natura 2000.

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DOI resolver: doi.org/10.5593/sgem2019/3.1/s12.023

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