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ABSTRACT Several global and regional high-resolution precipitation products have been released over the past decade by combining precipitation estimates from various sources including satellite-based measurements and gauge-based observations. With relatively few validation studies over the Eastern Himalayan region, this study examined seasonal and interannual skills of four gridded precipitation products including the regional gauge-based APHRODITE (Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of Water Resources) and three near-global satellite-based products: Tropical Rainfall Measuring Mission ( TRMM), Climate Prediction Centre (CPC) MORPHing ( CMORPH), and Climate Hazards Group InfraRed Precipitation ( CHIRP) using in-situ rain gauge data from Bhutan for the period 1998-2012. Principal component analysis ( PCA) was used to assess the dominant rainfall patterns over Bhutan. An attempt has also been made to correct precipitation biases in the satellite-only products using a gamma ( γ)-based distribution approach. Results indicated that APHRODITE and satellite-based precipitation products were able to adequately capture the spatio-temporal patterns of rainfall variability over Bhutan. Extreme precipitation events and extreme drought periods were well captured with very good correlations (>0.5). APHRODITE and TRMM 3B43v7 were remarkably similar, whereas satellite-only products ( CMORPH and CHIRP) highly underestimated (20-60% or 200-450 mm month−1) monsoon rainfall over Bhutan. While TRMM 3B43v7 still underestimated monsoon rainfall (by ∼25%), it has significantly improved the seasonal bias (by 20-40%) from its previous version (TRMM 3B43v6). CHIRP performed relatively better in the high rainfall regions but indicated very low correlations over mountainous regions and during the pre- and post-monsoon season. The bias correction approach indicated best results for TRMM 3B43v6 (up to 33%) in the Southern Foothills, whereas satellite-only products improved only moderately (5-20%). [ABSTRACT FROM AUTHOR]

ABSTRACT The estimation of large-scale evapotranspiration ( ET) is complex, and typically relies on the outputs of land surface models ( LSMs) or remote sensing observations. However, over some regions of Africa, inconsistencies exist between different estimations of ET fluxes, which should be investigated. In this study, we evaluate and combine different ET estimates from moderate-resolution imaging spectroradiometer ( MODIS), Global Land Data Assimilation System ( GLDAS) and terrestrial water budget ( TWB) approaches over the Volta Basin, West Africa. ET estimates from water balance equation are obtained as residuals from monthly terrestrial water-storage ( TWS) changes derived from Gravity Recovery and Climate Experiment ( GRACE), Tropical Rainfall Measurement Mission ( TRMM)'s rainfall data, and in situ discharge from Akosombo Dam (Ghana). An averaged estimation of ET time series is derived from all the ET estimations under study, while taking into account their uncertainties. The resulting ensemble-averaged ET was then used to assess each of the individual ET estimates. Overall, out of the seven investigated ET estimates (two from the water balance approach of which one considers water storage using GRACE-derived TWS and the other ignoring it, four from GLDAS and one from MODIS), only MODIS (28.12 mm month-1), GLDAS-NOAH (32.74 mm month-1) and TWB (32.84 mm month-1) were found to represent the range of variability close to the computed averaged reference ET (30.25 mm month-1). ET estimations inferred from MODIS were also found to represent relatively lower magnitude of uncertainties, that is, 3.99 mm month-1 over the Volta Basin (cf. 7.06 and 18.85 mm month-1 for GLDAS-NOAH and TWB-based ET estimations, respectively). [ABSTRACT FROM AUTHOR]

The changing climatic patterns and increasing human population within the Lake Victoria Basin (LVB), together with overexploitation of water for economic activities call for assessment of water management for the entire basin. This study focused on the analysis of a combination of available in situ climate data, Gravity Recovery And Climate Experiment (GRACE), Tropical Rainfall Measuring Mission (TRMM) observations, and high resolution Regional Climate simulations during recent decade(s) to assess the water storage changes within LVB that may be linked to recent climatic variability/changes and anomalies. We employed trend analysis, principal component analysis (PCA), and temporal/spatial correlations to explore the associations and covariability among LVB stored water, rainfall variability, and large-scale forcings associated with El-Niño/Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Potential economic impacts of human and climate-induced changes in LVB stored water are also explored. Overall, observed in situ rainfall from lake-shore stations showed a modest increasing trend during the recent decades. The dominant patterns of rainfall data from the TRMM satellite estimates suggest that the spatial and temporal distribution of precipitation have not changed much during the period of 1998-2012 over the basin consistent with in situ observations. However, GRACE-derived water storage changes over LVB indicate an average decline of 38.2 mm/yr for 2003-2006, likely due to the extension of the Owen Fall/Nalubale dam, and an increase of 4.5 mm/yr over 2007-2013, likely due to two massive rainfalls in 2006-2007 and 2010-2011. The temporal correlations between rainfall and ENSO/IOD indices during the study period, based on TRMM and model simulations, suggest significant influence of large-scale forcing on LVB rainfall, and thus stored water. The contributions of ENSO and IOD on the amplitude of TRMM-rainfall and GRACE-derived water storage changes, for the period of 2003-2013, are estimated to be ∼2.5 cm and ∼1.5 cm, respectively. [ABSTRACT FROM AUTHOR]