Hydrological Modelling In Arid Catchments With Data Scarcity (Ferghana Valley, Central Asia)

With the global warming it is essential to study water resources in the arid regions like the Ferghana Valley (~79,000 km² with surround highland) in Central Asia, where agricultural production heavily depends on irrigation. Main water resources for irrigation are currently provided by the Naryn and Karadarya river systems. The surrounding mountainous areas of the valley with their large glacial water storages play a big role in the annual water balance of these rivers. The decrease of glaciers due to the global temperature rise will most likely lead to the runoff reduction. An impact analysis of the climate change on the water resources is of utmost importance both for economic as well as ecological issues in the region. The overall objective of the study is to estimate the relative contribution of small-sized catchments with mainly precipitation driven runoff (in total 19 catchments) and the large Naryn and Karadarya rivers which are dominated by glacial melt water to the Ferghana Valley water balance under current and future climatic conditions. Any future model-based prediction of the water resources availability is depended on a thorough understanding of the hydrological cycle under current conditions. Therefore, the aim is at investigating the water balance of the small surrounding catchments using the conceptual HBV-light model. In this study it is shown the model setup for the Kugart River (1,010 km²), Kurshab River (2,010 km2), Akbura River (2,260 km²) and Shakhimardan River (1,180 km²) catchments in Kyrgyzstan. Model setup is highlighted especially in the view of data availability limitations. Thus, the MODAWEC model that calculates daily meteorological data from monthly is applied for the four studied catchments (the correlation coefficient for generated and measured average temperature varies from 0.84 to 0.91). The HBVlight model is employed successfully for measured allocated climate data and generated (temperature) allocated data to the central part of the basins with the Nash-Sutcliffe efficiency coefficient (NSE) both for calibration (1980-1983) and validation (1984-1985) periods in the range of 0.50 to 0.89 for the studied basins. The acceptable parameter sets for the model after using of threshold (NSE ≥ 0.50, NSE log ≥ 0.50, and the difference in annual water balance ± 20 mm) ranges from 21 to 558. Thus, the hydrological modelling using generated meteorological data and the HBV-light model will be applied for the remaining 15 small catchments that discharge into the Fergana Valley. And for the assessment of climate change impact on the water resources in the Ferghana Valley it is planned to apply the different climate change scenarios in the near future.