Climate Forcing

Multi Time and Space Scaling

The climate of Bhutan varies depending on the altitude. The climate can vary considerably between the valleys and within the valleys depending on levels of altitude, and aspects. Rainfall, in particular, can differ considerably within relatively short distances due to rain shadow effects. Monsoon is the main climatic factor in the south and it lasts from mid-June to September bringing 60-90% of the annual precipitation. Precipitation ranges from 2500 mm in the south to less than 500 mm above 4000 m annually. Average precipitation is roughly estimated around 1150 mm/year. The country receives rains throughout the year, except from November to January, with the maximum precipitation occurring between June and July. Out of total precipitation received, surface runoff constitutes 76%, 5% is as snow, and infiltration comprises 19% (RRCAP, 2012).

There is no “one” dataset that perfectly describes climate. Here three data sets were compared, for their implications for modelingriver flow and flow elasticity. The datasets included the NCEP/NCAR referred to as NCEP, Weather Research and Forecasting - WRF and ERA Interim - ERA. The NCEP and WRF data preparation were described in detail in Sonessa et al. (2012 – to be submitted). The only difference here the data has 1/24 latitude-longitude spatial resolution. The NCEP dataset ranges from 1948 – 2006, while the WRF dataset is from 1998 through 2007. The ERA data was also described in Sonessa et al. (2012 - to be submitted). However, the dataset used here runs from 1979 through 2011, while in Sonessa et al. (2012) it was from 1989 – 2006. Besides, the data used in Sonessa et al. (2012 – to be submitted) are water balance terms (precipitation, runoff and evapotranspiration).

Since the time ranges of the three datasets are different, we used the VIC run results from 1999 to 2006 to compare the simulated flows with observed flows to examine which dataset is best in the simulation.