| Summary: | The smallest magnitudes from a series of daily average-streamflows every month are selected to form a new series of data called a series of monthly minima from daily averagestreamflows or then just simply called the monthly minimum-streamflows. The present study uses these monthly minimum-streamflows to determine a drought index in terms of duration and deficit streamflows of successive drought in every watershed in West Sumatra Province. Both terms of drought index are determined by using the theory of runs with a 5-year average-period. So far, we successfully collect series of the daily average-streamflows for 19 watersheds with a minimum length of 20 years. The resulting indices are then mapped using the geographical information system ArcGIS. The drought indices are expressed in 4 levels of drought: normal (green), mild (blue), moderate (yellow) and severe (red). The study results show that the river or watershed with the longest droughtduration is Batang Anai, i.e. 33 months (severe level), with a cumulative deficit-streamflows of 143.26 m3/s. The river with the shortest drought-duration is Batang Siat, i.e. 11 months (mild level), with a cumulative deficit-streamflows of 44.64 m3/s. The average drought-duration for all corresponding rivers is 20 months (mild level) with a cumulative deficit-streamflows of 131.57 m3/s.
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