Drought analysis under climatic variability of Latur zone of Marathwada region

Introduction

The major source of water available either for agriculture or for human consumption is obtained from the rain. Rainfall is one of the most important natural inputs in many hydrologic processes. South-West monsoon, North-East monsoon, cyclonic depressions and local storms contribute to rainfall in different degrees in various rainfall regions of the country. Due to high temperature of summer, the moisture-laden south-west monsoon originates from the vast expanse of the Indian Ocean and enters the Indian sub-continent from the south-west. These south-west monsoonal winds increases from June to July and begins to weaken in September, especially in north India. By the first week of July, the monsoon is established all over the country, withdrawal of the monsoon starts in September in north India and there is rapid decrease of rainfall towards the end of month. Rainfed agricultural practices significantly impact the economy of developing countries; however, these practices are highly vulnerable to the effects of weather and climate (Rockstrom, 2002) [7] . The dates of onset of monsoon and withdrawal are different at different parts of the country. The crucial month for agriculture is July and August and the fate space of rain fed kharif crops largely depends upon the amount and distribution of rain specially during these two months.The variation of onset explains the significant variation in season duration since the onset date is more variable than the end date of the rains. Early onset of rains, relative to the mean date of onset for a given location, results in a longer growing season (Sivakumar, 1988) [9] in most of the state the percentage of irrigation is very low. In Maharashtra percentage of total irrigated area to total cropped area is 12.82. In Marathwada region this percentage of total irrigated to total cropped area is only 10.13 leaving about 90 percent area at the whim of monsoon. Marathwada is generally known to be drought prone area in Maharashtra. Precipitation is very uncertain in this region and sometimes suffers from severe droughts.

In such conditions only the knowledge of average annual rainfall is not useful in deciding cropping pattern. With growing emphasis on profitable crop production in such rainfed areas, knowledge of distribution of dry spells during monsoon season assumes an important role, it is important to know the chance of occurrence of dry spell during the critical period of lifecycle of the crops for planning the sowing periods and deciding the varieties of different crops. This helps the farmer in judicious utilization of soil moisture by way of crop planning. The rainfall during the monsoon is very uncertain and its distribution within growing season is not uniform. Delayed onset of monsoon, limiting magnitude at onset, breaks in rainfall and early cessation of rainfall are common phenomena. A break in rainfall continues from a few days to several weeks. The important characteristics of rainfall influencing production from rainfed farming are the date of onset of monsoon, the duration of rainy spells, the dates of occurrence and duration of intervening dry spells and distribution of weekly minimum rainfall and the number of rainy days. The occurrence of certain amount of rainfall at crucial times can determine the success or failure of a crop. Drying of crops, germination of seeds, disease during its growing period applying irrigation, fertilizer pesticides are some important agricultural activities for which probability of various sequences of wet and dry days may be used to determine the possible economic gains and losses. Rainfall during the monsoon period is not uniform. Breaks in monsoon are common phenomena during the monsoon period. A break continues from a few days to several weeks. Knowledge of the distribution of dry spells during the monsoon period is very much essential for successful management of agriculture. Short period rainfall probability analysis brings out the numbers of years of crops success and duration of crop growing period so that suitable crops may be chosen to get optimum yield. Runs of wet and dry spell helps to identify the duration of stress period. (Biswas, 1981) [2] . Variation in rainfall distribution patterns is the major reason for increasing the probability of occurrence of drought like situation in the country. India stands first among the countries that practice rain fed agriculture both in terms of extent (86 M ha) and value of production (Srinivasa, 2015) [8] . Wet and dry spell helps to identify the duration of surplus water and water stress period. Information on dry spell analysis plays an important role in proper utilization of available rainwater resources. Marathwada region of Maharashtra state, comprises districts Hingoli, Nanded, Latur, Parbhani, Jalna, Beed, Aurangabad and Osmanabad. The area in the region mostly falls under assured rainfall zone, though 15 to 20% falls under low and moderately high rainfall zone each. Under such climate change and aberrant weather situation, crop planning and management should be based on probability of rainfall occurrence, dryspell and available soil moisture analysis. Understanding the events of occurrence of dry spell and wet spell is crucial to decrease the adverse effects of dry spell at sensitive crop development stages. The probable behavior of rainfall was studied by many researchers (Kumar, 2007; Chakravorthy and Mandal, 2008; Chand, 2011; Jakhar, 2011) [6,3,4,5] .

Materials and Methods

Location

The present study is confined to Marathwada region.

Marathwada is one of the four political regions in the state of Maharashtra. Jawar, Sunflower, are the most important crops grown on large scale all over Latur zone of Marathwada region. There are 56 rain gauge station in Marathwada. Amongst them, 4 stations of Latur zone are Parbhani, Nanded, Latur and Hingoli, were selected for detailed analysis. The names and locations of the rain guage stations selected for analysis are given in table 1.

Data collection and processing

The daily rainfall data for the 4 rainguage stations of Latur zone of Marathwada region were obtained for the period 1981 to 2011 from the Indian Meterological Department, pune. The data collected for 31 years.

Concise Rainfall data

For making the daily rainfall data obtained for various stations to be concise. The number of rainy days for each month for every year were also obtained.

Onset of Effective Monsoon

There is a need for identifying "Effective Monsoon" as 'commencement of sowing rains' distinct from premonsoon showers. Because premonsoon rains cannot be considered as effective monsoon for agriculture operations, particularly because these rains are followed by long dry spells which may affect the germination of seeds resulting in crop failure if sowings are under taken immediately after these showers.

Determination of dates of OEM

The concept developed by Ashok Raj (1979) [1] on onset of effective monsoon and dry spells was adopted in the present study. Effective monsoon is that monsoon which leaves enough moisture to supports agricultural operations. If the average daily evaporation is e mm and after a prolonged dry spell, if it rains on a particular day an amount of r mmof rain, it is assumed that only (r-e) mm of rain will be available for the soil that day. If it rains on the subsequent days, the evaporation loss will be less than e mm. In the light of this, the rainfall of seven-day evaporational demand, is designated as the effective monsoon. Accordingly, the date of commencement of a 7 days spell satisfying the following criteria can be defined as the date of onset of effective monsoon. 1. The first day's rain in the seven days spell should be more than the average daily evaporation (e) of the place. 2. The total rain during the seven days spell should not be less than (5e+10) mm. 3. At least four out of these seven days should be rainy days with not less than 2.5 mm of rain each day. A day is called a rainy day if the rainfall of that day is more than or equal to 2.5mm.

The dates of onset of effective monsoon for every year for each station were determined by applying the above three criteria. After identifying the date of onset of effective monsoon xi(i=1,2,3……n) in the Ith year for a particular rain guage station, the mean date m is computed as follows :

m =∑xi/n (from i=1 to n) where, n is the number of years.

Determination of Dry spell and Wet spell

The dry spells were found out by applying the criteria stated by Ashok Raj (1979) [1] . The interval between the end of the 7-days spell, beginning with the onset of effective monsoon and another rainy day with 5e mm or more of rain or the commencement of another 7-day rainy spell satisfying the third criteria stated in above paragraph with a total rainfall of 5e mm or more during this spell is called as the first dry spell similarly other dry spells are found.

The interval between the OEM and the beginning of first critical dry spell is called the first wet spell. The subsequent wet spells are defined as the interval between two critical dry spells. thus, the wet spells are spells of prolonged rain with possible intervening dry spells of duration less than the value depending on crop-soil complex of the region, which makes the dry spell critical.

Critical dry spell (CDS)

If the duration the dry spell occurred during the monsoon season exceeds a certain period depending on the crop-soil complex of the region, the dry spell is called the first critical dry spell. Duration of 10 days was considered to classify the dry spell as critical during this study. There occurs more than one critical dry spell during every year. The critical dry spells were obtained for every year for each station.

The mean dates of starting of critical dry spells were obtained by the same procedure adopted for obtaining the mean dates of OEM. The isohyets were drawn for the dates of commencement of CDS and its durations.

Results and Discussion

Record of daily rainfall data for 31 years for Latur zone of Marathwada region that includes Parbhani, Latur, Hingoli, Nanded districts were obtained from the Deptt. of Agricultural Meteorology, M.A.U., Parbhani and Indian Meteorological Department Pune. Data were analyzed to determine rainfall characteristics influencing agricultural operations and irrigation management. The characteristics includes mean monthly rainfall, average weekly rainfall (AWR) and average annual rainfall. Daily rainfall and evaporation data of 31 years were used for determining the dates of onset of effective monsoon, critical dry spells and wet spells. The data were also analyzed for probability of occurrence of dry spell during crop developmental stages.

Analysis for Parbhani station Analysis of Rainfall data

The variations in annual rainfall and number of rainy days of Parbhani for 31 years (1981-2011)

Onset and end of effective monsoon

The rainfall data of 31 years (1981-2011) was taken in account. Daily rainfall and evaporation data of 31 years for Hingoli station from 1981-2010 were analyzed to find out the dates of onset of effective monsoon (OEM) and dates of withdrawal of monsoon during individual years. From the table 12, it is seen that effective monsoon starts from first week of June to third week of July. It is also observed that effective monsoon ends in between last week of September and third week of October.

Critical dry spells (CDS)

When the duration of dry spell exceeds a certain value depending on crop-soil complex of the region, it is called as critical dry spell. The critical value of duration of dry spell for Hingoli station was considered as 10 days. As shown in table 13. The mean dates of critical dry spell were July 09 with mean duration of 17 days for first CDS, August 23 with mean duration of 20 days for Second CDS and September 14 with mean duration of 21 days for third CDS for Hingoli station.

Summary and Conclusion

The daily rainfall and evaporation data of the four rainguage station namely Parbhani, Nanded, Hingoli and Latur were obtained for the analysis from the Department of Agricultural Meterology, VNMKV, Parbhani and Indian Meterology Department, Pune. The dates of onset and end of effective monsoon were determined for individual years by applying the criteria started by Ashok Raj (1979) [1] . Also mean dates of OEM and end of monsoon with standared deviation were determined for each station. Dry spell analysis was done by applying criteria stated by Ashok Raj (1979) [1] . Also mean dates of OEM and end of monsoon with were determined for each station, the critical dry spells were found during every year. Mean dates of critical dry spell along with their mean durations were also determined. The average dates of starting and ending of wet spell were also determined for each station. Following are the specific conclusions of the study. The average annual rainfall at Parbhani, Latur, Nanded and Hingoli stations was recorded as 872.53mm, 804.90mm, 806.30mm and 987.06 mm. 1. The average numbers of rainy days were found to be 41.

Acknowledgement

AcknowledgementsThe daily rainfall and evaporation data of the four rainguage station namely Parbhani, Nanded, Hingoli and Latur were obtained for the analysis from the Department of Agricultural Meterology, M.A.U. Parbhani and Indian Meterology Department, Pune.

References

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