Phaltan Weather, and to Identify Possible Trends Since 1983, Especially Warming
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Long term weather trends in Phaltan, Maharashtra A. Jacob1 and Anil K. Rajvanshi 2 1 French intern at NARI, student from Ecole Centrale de Lyon, Ecully 69130, France. 2 Director NARI, Nimbkar Agricultural Research Institute (NARI), Phaltan 415523, Maharashtra, India; email:[email protected] Abstract This study aims at analysing the meteorological data collected by Nimbkar Agricultural Research Institute (NARI) since 1983. The main objectives were to provide average figures and curves of Phaltan weather, and to identify possible trends since 1983, especially warming. Results show that there is indeed a clear warming trend, but it seems to be influenced by changes in the surroundings of the station (microclimate). Wind velocity and evaporation have also slightly decreased. Increase in plant cover in Phaltan area might have played a role. Keywords: climate change, rainfall trend, temperature trend, weather composites, rural area Knowledge of meteorological conditions is crucial to any agricultural work. Apart from the obvious rainfall and temperature factors, evaporation, wind and humidity are also affecting the way plants grow0. Usually climate is of less importance because of its very large timescale, but with the quick changes induced by the industrial era it may become a source of concern and a parameter to take into account. The aim of this study is thus to provide figures as well as composite (average) curves for the main meteorological parameters and identify possible trends. Only the most significant results have been presented here. Nimbkar Agricultural Research Institute (NARI) has been collecting meteorological data since 1983. The weather station is located in Phaltan town (Satara district, Maharashtra) at 18° latitude and 750m above sea level. It is currently recording 11 parameters daily (minimum and maximum temperature, minimum and maximum relative humidity, rainfall, pan evaporation, wind speed at two different heights, wind orientation and nature of sky). The solar radiation has been Figure 1 Location of Phaltan4 recorded between from 1985 to 1991 and from 2000 to 2003. ©NARI – September 2006 1/7 The average weather data is given in table 1. Table 1 Average weather of Phaltan weather Parameter Instrument used Value Mean daily maximum 33.5 °C Min/max Temperature Mean daily minimum thermometer 18.8 °C Mean daily average 25.1 °C Yearly rainfall 521 mm/y Mean rainfall 8.12 mm/d Rainfall Class A raingauge intensity Number of rainy days 64 d/y Wind Mean velocity Anemometer 5.06 km/h Mean daily maximum 81.6 % Relative Class A Mean daily minimum 36.7 % humidity hygrothermograph Mean daily average 59.1 % Mean daily 5.40 mm/d Evaporation Pan evaporation Yearly radiation Total radiation 1549 kWh/m²-y Solar radiation Mean daily radiation pyranometer 4.77 kWh/m²-d Composites for temperature, rainfall and solar radiation are given in figures 2, 3 and 4. The standard deviations of the values from all the years are shown in figures 2 and 4. 45 40 35 Daily max 30 Daily min 25 Daily 20 average 15 Air temperature (°C) 10 5 0 JFMAMJJASOND Month Figure 2 Temperature composite ©NARI – September 2006 2/7 14 88% 12 41% 10 14% 45% 8 6 Rainfall (mm/d) Rainfall 4 2 0 JFMAMJJASOND Month Figure 3 Rainfall composite 8 7 6 5 Solar radiation 4 3 2 Solar radiation(kWh/m²-d) 1 0 JFMAMJJASOND Month Figure 4 Solar radiation composite Figure 3 indicates that most of the rainfall falls during 5 month (June, July, August, September and October). Two peaks correspond to onsetting and receding monsoons. Phaltan gets most of its rainfall during receding monsoon. Thus second peak is much more significant, accounting for 41% of yearly rainfall in 43 days only. As most regions in India, rainfall is highly concentrated with an average of only 64 rainy days in the year and 72% of yearly rainfall falling in one fifth of the rainy days. These heavy downpours are difficult to harvest because of the surface runoff. Besides, yearly rainfall at Phaltan is 521mm which is quite low compared to the national average of 1280mm2. Moreover, the region is drought-prone as shown by ©NARI – September 2006 3/7 the coefficient of variability of yearly rainfall of 35% which is quite high. Efficient water harvesting technologies are thus critical to fulfil irrigation and drinking water needs throughout the year. 2 1,8 1,6 1.45°C increase 1,4 1.07°C increase 1,2 0.69°C increase 1 0,8 0,6 r2=0.62 Standard error of estimate=0.25°C Variation from 1983value (°C) 0,4 0,2 0 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Years Figure 5 Temperature trend (average) 4 3 y = 0.0676x + 0.6428 r2 = 0.4947 2 y = 0.0496x + 0.4463 r2 = 0.3334 1 y = 0.0219x - 0.5455 0 r2 = 0.1058 Winter -1 (Oct-Jan) Variation from 1983 value (°C) Summer -2 (Feb-May) Monsoon 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 (Jun-Sep) Years Figure 6 Seasonal temperature trends (average) Trends for different weather parameters are given in figures 5 to 11. Figure 5 shows a warming trend with a variation comprised between 0.69°C and 1.45°C with a 95% confidence level and an average estimation of 1.07°C. These figures are comparable to those in Indian cities3. But since plant cover has increased in the region, the temperature should have been reduced. A possible explanation is that our 23 years’ span is not sufficient to rule out “natural” cyclical variations, for which at least 50 ©NARI – September 2006 4/7 years would be needed3. Seasonal trends in figure 6 reveal a strange phenomenon: while average temperature is increasing for both winter and summer, it remains more or less constant for monsoon. This fact does not have any simple explanation since yearly rainfall, which occurs mostly during monsoon season, has not increased significantly (figure 7). Moreover seasonal average wind speeds have decreased at the same rate. But these differences in temperature increase tend to prove that the high increase in average temperature is not due to instrument errors. 1000 900 800 700 y = 3.3293x + 480.6 2 600 r = 0.0152 500 Rainfall (mm/y) Rainfall 400 300 200 100 0 3 6 8 0 2 4 6 9 1 3 5 8 85 8 87 8 89 9 9 9 9 98 9 00 0 02 0 0 9 9 9 9 9 9 9 0 0 1 1984 1 19 1 19 1 19 1991 19 1993 1 1995 1 1997 1 19 2 20 2 20 2004 20 Years Figure 7 Rainfall trend (yearly) 30,00 25,00 Daily average ) 20,00 /h m Daily max (k y it 15,00 oc l e V 10,00 5,00 y = -0.2842x + 8.4742 r2 = 0.8062 0,00 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Years Figure 8 Wind velocity trends The wind trend in figure 8 shows a steady decline since 1983. It might be a consequence of increase in plant cover in the region. Without green cover solar radiation heats the ground which creates more wind. Planting of trees in the close ©NARI – September 2006 5/7 surroundings (approx. 20m) of the weather station might have reinforced this trend. 100 90 y = 0.4904x + 75.672 2 80 r = 0.3623 Daily max 70 Daily 60 y = 0.3116x + 55.407 average r2 = 0.3277 50 Daily min 40 Relative humidity (%) humidity Relative y = 0.1329x + 35.142 R2 = 0.0844 30 20 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Years Figure 9 Humidity trends Average humidity has increased of 7.2% but the coefficient of determination is only 0.33. Thus, more data is needed to validate or refute this trend. An increase in humidity could again be explained by the increase in biomass in the region. 20 18 16 14 Daily max 12 Daily 10 average 8 6 Evaporation (mm/d) 4 y = -0.1205x + 6.8454 r2 = 0.6415 2 0 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Years Figure 10 Evaporation trends ©NARI – September 2006 6/7 Figure 11 shows a clear decreasing trend for average evaporation. Evaporation is a function of temperature, wind speed and humidity. A good correlation can be found between wind and evaporation trends indeed since their coefficient of correlation is 0.87. Possible increase in humidity might have also played a minor role in this trend but the coefficient of correlation between the two parameters is only -0.34. Finally, the increase in temperature should have tempered the decreasing trend in evaporation but it didn’t seem to have much influence. Even though our data may be inadequate to ascertain trends, we have still recorded clear tendencies towards warming and reduced wind speed and evaporation. Increase in vegetation in the surroundings of Phaltan might have played a role in wind and evaporation trends, but some facts such as the high increase in temperature and the constant monsoon temperature remain unexplained. Composites and average figures can still be used fruitfully by farmers to plan their crops and anticipate rainfall and temperature variations.