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An erratic monsoon with late spikes

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RG_IMD_rain_deficit_chart_20140924From the first week of June 2014 until the middle of September 2014, there have been floods and conditions near drought in many districts, but for India the tale of monsoon 2014 comes from individual districts and not from a national ‘average’ or a ‘cumulative’.

The weekly rainfall variation table for Maharashtra's districts. The period of the last week of August and the first two weeks of September is the only period during which these districts received rainfall at or above normal. But overall, the second deficient category, coloured light rose, dominates (this table uses my modified monsoon measure methodology, see text for link)

The weekly rainfall variation table for Maharashtra’s districts. The period of the last week of August and the first two weeks of September is the only period during which these districts received rainfall at or above normal. But overall, the second deficient category, coloured light rose, dominates (this table uses my modified monsoon measure methodology, see text for link)

This revealing chart tells some of that tale. It shows that for the first six weeks of monsoon 2014, most districts recorded rain below their normals for those weeks.

The lines are percentile lines; they tell us what percent of districts recorded how much rainfall in a monsoon week relative to their normals for that week. This chart does not show how much rain – it shows distance away from a weekly normal for districts.

The left scale is a percentage – higher percentages indicate how much above normal districts recorded their rainfall, negative numbers show us how much below normal their rainfall was.

The dates (the bottom scale) are for weeks ending on that date for which ‘normals’ and departures from normal were recorded. The P_01 to P_09 lines are the percentiles (10th to 90th) of districts in every week.

The typical IMD map of 'normal' rainfall measured by the meteorological sub-divisions. The detailed weekly tables give us a very different picture.

The typical IMD map of ‘normal’ rainfall measured by the meteorological sub-divisions. The detailed weekly tables give us a very different picture.

The district weekly normal is an important measure for matters like sowing of crop and issuing water rationing instructions in talukas and blocks. In the week ending 23 July for example, we see that the 60th percentile line spiked above normal, and this means that in that week only four out of ten districts all over India received the amount of rain it should have based on the average of the last 50 years.

The districts overview chart is distilled from the detailed weekly tables I have assembled (see the image of the Maharashtra table). For the whole country, what the districts tell us about the monsoon so far is a very much more detailed and insightful tale than the typical offering by the Meteorological Department (see India sub-divisional map). These weekly district tables are coded using my modified monsoon methodology, geared towards aiding decisions for local administrations especially for prolonged arid conditions leading to drought.

Written by makanaka

September 24, 2014 at 10:06

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