Using an integrated hydrological model to estimate the impacts of droughts in a semiarid transboundary river basin: the case of study of the Tijuana River Basin

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Abstract
The Tijuana River Basin is a transboundary basin located in a semi-arid region, vulnerable to droughts due to low precipitation, high evapotranspiration rates and a rapid population growth due to the international border between the United States of America and Mexico that increases water demand in the border cities. In this study, the impacts of drought periods were evaluated for the period of 1984-2016. First, drought periods were identified using two different indices: the Standardized Precipitation Index (SPI) and the Normalized Difference Vegetation Index (NDVI). Second, a hydrological model (Soil and Water Assessment Tool, SWAT) was set up and calibrated to estimate the water balance and assess drought impacts on the water availability in the Tijuana River Basin (TRB). Drought analysis was performed using precipitation from local observations as well as data from the Land Data Assimilation System (NLDAS) that allowed enhancing spatiotemporal analysis. Three major drought periods were identified in the TRB: 1999-2003, 2006-2008 and 2014-2015. Results indicated that the mean annual precipitation was reduced by 40% in the first drought period (with respect to the period 1984-2016) resulting in a 77% runoff reduction. The other two drought periods analysed, 2006-2008 and 2014-2015, showed lower precipitation reduction, 13% and 16%, respectively. This resulted in streamflow decreases of 44% and 66%, respectively. This work shows that the use of drought indices and SWAT modeling is a useful combination to assess the hydrological impacts of droughts in a semiarid basin. This methodology may be transferred to other regions in the world under similar climatological conditions and can be of help for stakeholders and water managers for water use planning.
Funding Information
  • Secretaría de Ciencia, Humanidades, Tecnología e Innovación (Programa de Becas para Estudios de Posgrado)
  • Fundación Ramón Areces (26th edition of grants for postgraduate studies)

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