Abstract:
Daily rainfall data of 1975-99 for nine talukas (Anjar, Bhachau, Bhuj, Lakhpat, Mandiv, Mundra, Nakhtrana, Naliya and Rapar) have been statistically analysed to study various aspects related with their spatial and temporal variation in the district. A critical look at study the onset of effective monsoon in the district showed that the mean date of effective monsoon varied during Jul 11(Mandvi) to Jul 27 (Rapar) with earliest on set of effective monsoon (p=0.68) during Jun 22 (Mundra) to Jul 3 (Bhuj). In general, for the entire district, the average onset of effective monsoon may occur during Jun 16 to Jul 12 with standard deviation of 26 days and it may cease around Sep 2. High standard deviation of 17 days (Bhachau, Mandvi) to 30 days (Rapar) showed inconsistent variation in daily rainfall of the stations. Mean date of withdrawal of monsoon ranged from Aug 20 (Lakhpat) to Sept 28 (Rapar). On an average each taluka experiences at least two critical dry spells (Table 2) during the monsoon period. The first critical dry spell of 23 days (Lakhpat, Rapar) to 38 days (Bhuj) is expected to start in second fortnight of July. Second critical dry spell ranging from 16 (Naliya) to 38 days (Nakhtrana) is expected to start mostly in August. In general the entire district may experience critical dry spells of 61 days duration comprising 29,28 and 20 days starting on Jul 13, Aug 5 and Aug 20 respectively. It indicates acute necessity of storing run-off water for the region to tackle the imminent water shortage problems of the crops. On an average rainfall during the three to four wet spells ranged in the district from 387 mm at Nakhtrana to 553 mm at Rapar. The first wet spell of the order of 186.4 mm at Rapar to 330.2 mm at Mundra may be harvested and stored in rain water harvesting structure. In general, for the entire district, about 523 mm of rain water can be harnessed and stored in water harvesting structures. Inconsistent variation in these talukas necessitate proper harvesting of rain water in the structure and its use in agricultural production. The paper also presents harnessable runoff based on USDA-SCS Curve Number method for the region which can be duly considered for improved agricultural water management strategies.
