Characterizing inter and intra annual variability in hydroclimatic extremes: The case of the Tempisque river basin in Northwestern Costa Rica.

Regional precipitation patterns are changing all around the world, bringing added stress to social, economic and environmental systems, and reshaping prospects for food, water and health security. This change, attributable in large part to the changing climate, has led to an alteration of the occurrence and magnitude of extreme hydrometeorological events like floods and droughts. To predict how climate extremes will change in the near future, it is important to first understand the nature of changes in the historic record and their potential drivers. The main goal of this research is to identify how extreme precipitation varies in northwestern Costa Ricas Tempisque river basin. This research is part of a larger interdisciplinary project aiming to understand the resilience of the coupled human-natural system of the Tempisque basin. The main economic activity of the area is agriculture such as sugar cane, rice, cantaloupe, Tilapia farms and cattle, which has suffered from poor management and extreme droughts and floods. Since water plays an important role to the livelihood of the people and the environment in this region, the variations in precipitation can help understand how the system changes and reacts to shocks such as floods and droughts. To characterize the spatial variability of extreme rainfall patterns, this study uses daily rainfall records at least 18 years in length from six meteorological stations distributed across the Tempisque river basin. Extreme precipitation is characterized using block maxima and peak over threshold approaches in extreme value theory for both excess rainfall and the duration of dry spells, a surrogate for drought. To evaluate potential global scale drivers of inter and intra annual variability, average and maximum monthly rainfall, as well as length of dry spells are linked to atmospheric teleconnections such as the El Niño-Southern Oscillation and the Atlantic Multidecadal Oscillation. Results from this research will help identify possible trends in climate variability in the area, improving the management and decision-making process involving water allocation, and ecosystem services.