DROUGHT MONITORING : ROLE OF IMD

1. DROUGHT MONITORING : ROLE OF IMD JAYANTA SARKAR IMD, PUNE

2. DROUGHT • is the consequence of a natural reduction in the amount of precipitation over an extended period of time, usually a season or more in length, often associated with other climatic factors (viz. high temperatures, high winds and low relative humidity) that can aggravate the severity of the event (WMO No. 869, 1997).

3. DROUGHT • METEOROLOGICAL DROUGHT • HYDROLOGICAL DROUGHT • AGRICULTURAL DROUGHT • SOCIO-ECONOMIC DROUGHT

4. METEOROLOGICAL DROUGHT • In India, according to India Meteorological Department, meteorological drought over an area is defined as a situation when the seasonal rainfall received over the area is less than75% of its long term average value. • It is further classified as "moderate drought" if the rainfall deficit is between 26-50% and "severe drought" when the deficit exceeds 50% of the normal.

5. HYDROLOGICAL DROUGHT • HYDROLOGICAL DROUGHT can be defined as a period during which the stream flows are inadequate to supply established use of water under a given water management system. • HYDROLOGICAL DROUGHT year can be defined as one in which the aggregate run off is less than the long-term average runoff. Most of the criteria developed for hydrological drought are specific to individual streams or river basins.

6. AGRICULTURAL DROUGHT It occurs when available soil moisture is inadequate for healthy crop growth and cause extreme stress and wilting. • AGRICULTURAL DROUGHT CATEGORIES • Early season drought • Mid season drought • Late season drought • Permanent drought • Apparent drought

7. SOCIO-ECONOMIC DROUGHT • Abnormal water shortage affects all aspects of established economy of a region. • This in turn adversely affects the social fabric of the society creating unemployment, migration, discontent and various other problems in the society. • Thus, meteorological, hydrological and agricultural drought often lead to what is termed as ‘Socio-economic drought’.

8. DROUGHT MONITORING BY IMD • IMD has been deleneating sub-divisionwise drought since 1875. In our country, a year is considered to be a DROUGHT YEAR in case the area affected by moderate and severe drought, either individually or together, is 20-40% of the total area of the country and seasonal rainfall deficiency during south-west monsoon season for the country as a whole is at least 10% or more. • When the spatial coverage of drought is more than 40% it will be called as ALL INDIA SEVERE DROUGHT YEAR. (Ref.: IMD Technical Circular No. 2/2007)

9. MONITORING AGRICULTURAL DROUGHT Aridity anomaly index AI = (PE- AE)/PE* 100 (210 stations) where,AI = weekly/fortnightly aridity index AE = Actual evapo-transpiration (thornthwaite,PE, ACTUAL RF, FC) PE = Potential evapo-transpiration (penman,TM, SOL RAD.,R.H., WIND SPEED) For the sake of computing anomaly, long term weekly/fortnightly values of aridity index are computed. The difference between actualAI in any week/fortnight of the crop season and the normal AI expressed as a percentage called aridity anomaly which represents water stress condition. Based on the AI the incidence, spread, intensification and cessation of different drought intensities on weekly/fortnightly basis is monitored. Following criteria are used in defining various agricultural drought intensities : Weekly/fortnightly Anomaly of AI Associated Drought Intensity 1 - 25 Mild 26 - 50 Moderate >50 Severe

10. THORNTHWAITE’S WATER BALANCE TECHNIQUE • WATER BALANCE REFERS TO THE BALANCE BETN. WATER INCOME(PPTN.) AND LOSS OF WATER BY EVAPOTRANSPIRATION CAUSING CHANGE IN SOIL MOISTURE AND RUNOFF. • BASIC EQUN. P= ET+CHANGE IN ‘S’ +RO • SOIL ACTS AS A MEDIUM FOR STORING WATER (UPTO A LIMIT) DURING EXCESSIVE RF AND RELEASING THE SAME (IN A RESTRICTED MANNER) AT OTHER TIMES FOR EVAP. AND TRANSPIRATION. • FOR WATER BALANCE COMPUTATION 3 PARAMETERS REQD.: ET, P, AWC (FC)

11. THORNTHWAITE’S WATER BALANCE TECHNIQUE • DURING THE PERIODS OF EXCESSIVE ‘RF’ THE BALANCE OF WATER, AFTER MEETING CROP DEMAND RECHARGES THE SOIL TILL ‘FC’ IS ATTAINED. ANY FURTHER ADDITION MEANS ‘RO’. • ‘AWC’ OF A PLACE DEPENDS ON THE TYPE OF SOIL AND THE ROOT ZONE DEPTH OF THE CROP. • DURING DEFICIENT ‘RF’ ‘SM’ IS USED FOR ‘ET’ PURPOSES. AS SOIL DRIES , ET RATE DECREASES. ACC. TO THORNTHWAITE, THE RELEASE OF MOSTURE FROM SOIL FOLLOWS THE FOLLOWING EQUN.: S=FC.exp –APME/FC S= Moisture remaining in the soil as storage

13. LEGENDS • Acc. P-PE = ACC. –VE VALUES OF (P-PE) • S= STORAGE • S*= CHANGE IN STORAGE • WD= PE-AE • WS= P-PE • RO= (‘WS’ of that month+’RO’ of the prev. month)/2

21. OTHER DROUGHT INDICES • DECILE APPROACH (COUGHLAN, 1987) • PALMER DROUGHT SEVERITY INDEX (PDSI) (PALMER,1965) • SPI (MCKEE et al.1993) • CMI(PALMER,1968)

22. DECILE APPROACH (COUGHLAN, 1987) • THE DECILE APPROACH IS A NON PARAMETRIC METHOD TO DESCRIBE THE DISTRIBUTION OF RAINFALL TOTALS. • ANNUAL RF TOTALS FOR A LONG SERIES OF YEARS ARE ARRANGED IN AN ASCENDING ORDER AND ARE THEN SPLIT INTO TEN EQUAL GROUPS. THE FIRST GROUP WOULD BE IN DECILE RANGE ONE, THE SECOND GROUP IN DECILE RANGE TWO ETC. • IT IS POSSIBLE IN A DECILE RAINFALL MAP TO SHOW WHETHER THE RAINFALL IS ABOVE AVERAGE, AVERAGE OR BELOW AVERAGE FOR THE TIME PERIOD AND FOR THE AREA CHOSEN.

23. PALMER DROUGHT SEVERITY INDEX (PDSI) (PALMER,1965) • PDSI IS BASED ON THE CONCEPT OF A HYDROLOGICAL ACCOUNTING SYSTEM, RELATES DROUGHT SEVERETY TO THE ACCUMULATED WEIGHTED DIFFERENCES BETWEEN ACTUAL PRECIPITATION AND THE PRECIPITATION REQUIREMENT OF EVAPOTRANSPIRATION. • THE PDSI IS CALCULATED BASED ON PRECIPITATION AND TEMPERATURE DATA, AS WELL AS THE AVAILABLE SOIL WATER CONTENT. FROM THE INPUTS, ALL THE BASIC TERMS OF THE WATER BALANCE EQUATION CAN BE DETERMINED, INCLUDING EVAPOTRANSPIRATION, SOIL RECHARGE, RUN-OFF AND MOISTURE LOSS FROM THE SURFACE LAYER. • PDSI IS MOST EFFECTIVE IN DETERMINING LONG TERM DROUGHT (SEVERAL MONTHS). NOT GOOD FOR SHORT-TERM DROUGHT MONITORING.

24. SPI (MCKEE et al.1993) • SPI HAS BEEN DEVELOPED TO QUANTIFY THE PRECIPITATION DEFICIT FOR MULTIPLE TIME SCALES. • IN SPI CALCULATIONS, THE LONG TERM PRECIPITATION RECORD FOR A DESIRED PERIOD IS FITTED TO A PROBABILITY DISTRIBUTION. IF A PARTICULAR RAINFALL EVENT GIVES A LOW PROBABILITY ON THE CUMULATIVE PROBABILITY FUNCTION,THEN THIS INDICATES A LIKELY DROUGHT EVENT. • ACCORDING TO SPI, A DROUGHT EVENT OCCURS ANY TIME THE SPI IS CONTINUOUSLY NEGATIVE AND REACHES A SPI VALUE OF -1.0 OR LESS. THE EVENT ENDS WHEN THE SPI BECOMES POSITIVE.

25. CMI(PALMER,1968) • CMI IS A METEOROLOGICAL APPROACH TO MONITOR WEEK-TO-WEEK CROP CONDITIONS. • CMI DEFINED DROUGHT IN TERMS OF THE MAGNITUDE OF COMPUTED ABNORMAL ET DEFICIT WHICH IS THE DIFFERENCE BETWEEN ACTUAL AND EXPECTED WEEKLY ET. • MORE EFFECTIVE THAN PDSI IN MONITORING SHORT TERM DROUGHT. • DIFFERS FROM PDSI IN THAT IT GIVES LESS WEIGHT ON THE DATA FROM PREVIOUS WEEKS AND MORE WEIGHT ON THE RECENT WEEK. • CAN BE USED TO COMPARE MOISTURE CONDITIONS AT DIFFERENT LOCATIONS. • CMI’S RAPID RESPONSE TO CHANGING SHORT TERM CONDITIONS MAY PROVIDE MISLEADING INFORMATION ABOUT LONG TERM CONDITIONS. FOR EXAMPLE, A BENEFICIAL RAINFALL DURING A DROUGHT MAY ALLOW THE CMI VALUE TO INDICATE ADEQUATE MOISTURE CONDITIONS, WHILE THE LONG TERM DROUGHT AT THAT LOCATION PERSISTS.

30. DROUGHT EARLY WARNING SYSTEM IN INDIA Breaks in the monsoon rains can be of different durations. Breaks of shorter duration like 5 to 10 days may not be of serious concern. But prolonged breaks of more than 2 weeks can create plant water stress leading to low productivity of crops. • The agricultural droughts caused due to prolonged breaks in the monsoon rains can be of different magnitudes and severity and affect different crops in varying degrees. • Application of meteorological information in terms of the frequency and probability of these breaks can be made to select a combination of crops of different durations in such a way that there is a time lag in the occurrence of their growth for appropriate inter-cropping systems.

31. LONG RANGE SEASONAL FORECAST OF INDIA METEOROLOGICAL DEPARTMENT • Indian economy is basically an agro-based economy. Agricultural planning of the nation is primarily dependent on the reasonable accurate prediction of total amount of rainfall from the beginning of June to the end of September. This kind of prediction comes under the category of Long Range Forecast (LRF). • The first operational LRF for seasonal monsoon rainfall was issued on June 4, 1886. • Presently, IMD issues a LRF based on statistical techniques.

32. Since 2003 IMD has been following a two stage forecast strategy for the LRF. • First forecast issued in April. • Forecast update issued end of June. • In 2004 dynamical forecasting system installed in IMD to produce experimental dynamical model forecast. • It suggests above normal rainfall over NE India and South peninsula and below normal rainfall over NW India. For the country as a whole the dynamical model suggests slightly above normal rainfall.

33. LRF-2007 1. Southwest monsoon seasonal rainfall • IMD’s LRF for 2007 SW monsoon season is that for the country as a whole the seasonal rainfall is likely to be 93% of the long period average (LPA) with a model error of +4%. 2. July rainfall • Likely to be 95% of its LPA (model error+9%) 3. Seasonal rainfall over broad geographical regions • Northwest India: 90% of its LPA(LPA = 612 mm) • Northeast India: 98% of its LPA(LPA = 1429 mm) • Central India: 96% of its LPA(LPA = 994 mm) • South peninsula: 94% of its LPA(LPA = 725 mm) (model error +8%)

34. REALIZED RAINFALL- MNSN 2007

35. BROAD GEOGRAPHICAL REGIONS for LRF • Northwest India: J&K, H.P, Punjab, Rajasthan, Haryana, Chandigarh, Delhi, Uttarakhand and U.P. • Northeast India: A.P., Meghalaya, Assam, Nagaland, Manipur, Mizoram, Tripura, Sikkim, West Bengal, Bihar and Jharkhand. • Central India: Gujarat, M.P., Chattisgarh, Maharashtra, Goa and Orissa. • South peninsula: Andhra Pradesh, Karnataka, T.N., Kerala, Lakshadweep and A&N Islands

36. PRESENTING DROUGHT INFORMATION IN AAS BULLETINS • THE GOAL IS TO ENABLE AND PERSUADE PEOPLE AND ORGANISATIONS TO TAKE ACTION TO MAXIMISE THE PROBABILITY OF SUCCESSFUL PRODUCTION IN AGRICULTURE, FORESTRY AND FISHERIES AND /OR MINIMISE THE POTENTIAL DAMAGE TO ESTABLISHED CROPS, FORESTS AND OTHER ASSETS. • THE ULTIMATE OBJECTIVE IS TO ENABLE GOVTS. AND ORGANISATIONS TO DEVELOP A PRO-ACTIVE RESPONSE TO DROUGHTS.

37. COMPONENTS OF DROUGHT INFORMATION • FOLLOWING COMPONENTS PRESENT A COMPREHENSIVE PICTURE OF DROUGHTS IN A GIVEN REGION: • TIMING OF DROUGHT • DROUGHT INTENSITY • DROUGHT DURATION • SPATIAL EXTENT OF A SPECIFIC DROUGHT EPISODE • RISK ANALYSIS OF THE PHENOMENON AND ITS LIKELY IMPACT ON AGRIL. PDN.

38. TIMING OF DROUGHT • DIFFICULT TO DEFINE DROUGHT ONSET AS IT IS A CREEPING PHENOMENON. SOME ATTEMPTS ARE: • ACC. TO BRITISH MET. OFFICE, AN ABSOLUTE DROUGHT BEGINS WHEN AT LEAST 15 CONSEQUTIVE DAYS HAVE GONE BY WITH LESS THAN 0.25mm OF RF ON ALL DAYS. • ACC. TO IMD, MET. DROUGHT OCCURS WHEN AN AREA RECORDS RF DEFIENCY OF MORE THAN 25% DURING SW-MNSN SEASON.

39. DROUGHT INTENSITY • IMD PROVIDES MET. DROUGHT INTESITY BASED ON RF DEFIENCY FROM NORMAL • PROVIDES AGRIL. DROUGHT INTESITY BASED ON ARIDITY ANOMALY INDEX VALUES.

40. DROUGHT DURATION • DROUGHT DURATION DEPENDS BOTH ON THE ONSET OF DROUGHT AND WHEN EXACTLY THE DROUGHT ENDS. • IT IS IMPORTANT TO EVALUATE CAREFULLY CONDITIONS THAT COULD SIGNAL THE END OF DROUGHTS, VIZ., RF ABOVE A GIVEN THRESHOLD, SOIL MOISTURE RECHARGE THAT WOULD ENABLE CROPS TO RECOVER ETC. • THE LENGTH OF THE TIME A DROUGHT PERSISTED IS A GOOD INDICATOR OF THE NATURE OF THE PROBLEM AND RELATES QUITE WELL TO THE DAMAGE IN AGRICULTURE.

41. SPATIAL EXTENT OF A SPECIFIC DROUGHT EPISODE • IT IS BEST DESCRIBED BY GENERATING DROUGHT MONITORING MAPS AS ARE BEING PRODUCED BY DRU, IMD USING ARIDITY ANOMALY INDEX (AAI).

42. RISK ANALYSIS OF THE PHENOMENON AND ITS LIKELY IMPACT ON AGRIL. PDN. • AS THE DROUGHT INFORMATION IS PRIMARILY TO ASSIST THE FARMING COMMUNITY IN MAKING OPERATIONAL DECISIONS REGARDING MANAGING THEIR FARMING SYSTEMS, IT IS IMPORTANT TO PROVIDE A SHORT ANALYSIS OF THE RISK OF AN ONGOING DROUGHT PHENOMENON AND HOW IT IS LIKELY TO IMPACT AGRICULTURAL ACTIVITIES. • CLOSE INTERACTION WITH THE EXTENSION AGENCIES ACTIVE IN A REGION COULD BE HELPFUL IN THIS REGARD. • PLANNING AGENCIES ALSO SHOULD BE INFORMED ABOUT THE IMPORTANT ASPECTS OF ONGOING DROUGHTS AND THEIR LIKELY IMPACTS TO ASSIST THEM IN MAKING APPROPRIATE ADJUSTMENTS IN THEIR REGIONAL/NATIONAL PLANS.

43. CONTINGENT CROP PLANNING FOR • DELAYED MONSOON ONSET GROWING SEASON LENGTH GETS SHORTENED, SHORT DURATION VARIETIES REQUIRED. SOMETIMES CROPS AFFECTED BY P&D PROBLEMS. • BREAKS IN MONSOON • POOR RAINFALL DISTRIBUTION IN SPACE AND TIME • EARLY CESSATION OF MONSOON RAINS SHORTER DURATION AND EARLY MATURING VARIETIES ARE NEEDED

44. CONCLUDING REMARKS IT IS POSSIBLE TO PROVIDE DROUGHT INFORMATION THAT ENABLES ACTION TO MAXIMISE THE PROBABILITY OF SUCCESSFUL CROP PRODUCTION AND MINIMISE THE POTENTIAL DAMAGE TO ESTABLISHED CROPS AND OTHER ASSETS. TO THIS END, INFORMATION SHOULD BE PROVIDED ON THE TIMING, INTENSITY AND DURATION AND THE SPATIAL EXTENT OF DROUGHTS. AN EQUALLY IMPORTANT ELEMENT OF DROUGHT EARLY WARNING SYSTEMS IS THE TIMELY AND EFFECTIVE DELIVERY OF THIS INFORMATION TO DECISION MAKERS. TO PROVIDE EFFECTIVE DROUGHT INFORMATION THERE SHOULD BE IMPROVED COLLABORATION AMONG SCIENTISTS AND MANAGERS TO ENHANCE THE EFFECTIVENESS OF OBSERVATION NETWORKS, DROUGHT MONITORING, PREDICTION, INFORMATION DELIVERY AND APPLIED RESEARCH. SUCH A COLLABORATION COULD HELP FOSTER PUBLIC UNDERSTANDING OF AND PREPAREDNESS FOR DROUGHT.

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