A Time Series of the Helmand River
The objectives of this subtask are to:
- Develop a time-series model for explaining monthly stream flow variability, given historical monthly stream flows, precipitation, and snow water equivalent data.
- Use the time series model to reconstruct a complete set of monthly stream flow for the study period of 1950 to present.
- Generate potential future monthly climatic inputs and stream flows and estimate the probabilities of future droughts or floods for a 50-year planning period.
Time series of rainfall estimate grids and snow water equivalent grids from 1981 until 2004 are serving as input to a stochastic model of monthly stream flow (see Figure 1 for distribution of Afghanistan rainfall stations for recent years).
Rain gage data were compiled for Afghanistan. Within the Central Southwest Asia window (24-35 N, 57-78 E), 157 long-term mean stations were used, and 108 monthly gages were also identified and formatted. Techniques were developed to produce orographically-enhanced rainfall estimates, and the assembly of time series grids of meteorological data was completed. Block kriging was used to combine the orographic precipitation with station data and reanalysis climate fields to produce a 45-year (1960-2004), daily, 0.1� time series of precipitation for the region. Snow water equivalent grids were created for 2005, 2004, and 2003, as well as for 1957, 1958, and 1959 (years for which stream flow records exist.
