EVALUATION OF TEMPORAL AND SPATIAL CLIMATIC VARIABILITY OVER INDIAN HIMALAYA

Abstract

The Indian Himalayas, the originating point of many important rivers, plays a vital role in controlling the weather of India. Despite this fact, the climate of Indian Himalayas is less studied because of its inaccessibility and hilly terrain that makes the data on meteorological and hydrological variables scarce. Mountains provide freshwater to half of the world's population and are home to half of all global biodiversity hotspots. Some of the questions which require a scientifically derived answer are as follows: (i) What will be the impact of climate -change in mountains and their adjacent lowlands? (ii) Where will the change take place and who will be most affected? To find the answer of the above questions, the Indian Himalayas where very limited studies have been undertaken was selected as the study area. The present study has been taken up with the following objectives: 1. To analyze short-term and long-term dependence in the climate parameters 2. To study spatial and temporal trends in the climatic variables 3. To search for the evidences of short-range and long-range periodicity/hidden periodicity 4. To study the effect of climate change on the river discharge of a typical Himalayan river basin Monthly meteorological data viz., maximum and minimum temperature, rainfall, number of rainy days and wind speed of varying length (22-59 years) for the period from 1933 to 2003 were procured from India Meteorological Department (IMD), Pune, for 23 selected stations (16 for wind speed) representatives of Indian Himalayas. For Satluj River basin daily maximum, minimum temperatures for six stations, rainfall data for eight stations, snowfall data for four stations and; discharge data for Bhakra gauging station were collected for the period 1985-2002 from the Bhakra Beas Management Board (BBMB), Nangal Township (Punjab), India. Altogether 14 (13 for short-term and Hurst's H for long-term) tests, were used to determine the existence of statistically significant dependence structure in the annual series of climatological variables. Majority of the series indicated presence of short-term dependence where as conditional probabilities of existence of only long-term dependence were, found to be negligible. The dependence was more pronounced in high altitude stations and stations with long records. Spatially, the eastern Himalayas show more dependence as compared to other regions of the Indian Himalayas. The Mann-Kendall's test with boot strapping technique (1000 runs) and Linear regression test were applied using HYDROSPECT software to detect significant trends and magnitudes in the climatological variables. The trend test results were spatially analysed using Inverse Distance Weighted (IDW) interpolation technique in ArcGIS 9.2 software package. Significant falling trends in mean minimum, mean temperatures and mean wind speed while significant rising trends in the diurnal temperature range were found over various regions of Indian Himalayas and in the entire Indian Himalayas. The monsoon season was found to be badly affected season for all the climatological variables. Significant decrease in annual and monsoon rainfall and significant increase in winter rainfall were revealed. Asharp declining trend throughout the Indian Himalayas was observed in mean wind speed. Spatial trend analysis also indicate significant decrease in the mean temperature, rainfall, number of rainy days andmean wind speed overthe western and central Himalayas. The Blackman & Tukey power spectrum method was used to determine short-range and long-range periodicities in the climatological variables. In the entire Indian Himalayas very few periodicities were observed in the quasi-biennial oscillation (QBO) region (period 2-3 years). Most of the periodicities were observed at 3.3, 5, 6.7 years i.e. outside the QBO region in all the climatological variables. However, in eastern Himalayas for mean minimum temperature and mean wind speed and; in central Himalayas for mean temperature range the significant periodicities were also observed at some other periodicities near the sunspot cycle (11 years ± 1 years) and few near the Hale solar magnetic cycle (22 ± 1 years) in eastern Himalayas for annual rainfall. Since its effect is almost the same as that of a random component, no meaningful predictions can be made even though some significant larger periodicities exist. Study of impact of climate change on water resources indicate a significant increase in annual mean temperature, mean maximum and mean minimum temperatures, unexpected VI warming of pre-monsoon season, decrease in rainfall, snowfall and discharge at Satluj River basin of western Himalayas. The warming was more pronounced in high altitude stations receiving winter precipitation in the form of snowfall. Decrease in discharge from 1986-2002 in the Satluj River basin, may be due to diminishing contributions of the glaciers. The study also shows that there is decrease in the extreme flows. However, a detailed analysis of estimating impact of climate change in extreme flows is very important for designing of water resources, irrigation and hydropower projects.