Vulnerability of Different Geomorphic Units to Deserts in Parts of Western Rajasthan-A Study Based on Remote Sensing and GIS

Cultivable land is the valuable natural resource which supports production food and fiber and many other essential goods required to meet human and animal needs for sustenance. However, it is facing serious threats of deterioration due to unrelenting human pressure and utilization incompatible with its capacity. Situation becomes more serious for the nation like India, where to cop up with agriculture production demand, large fertile land is required. A serious threat to this is desertification. Katyal and Vlek describes desertification is a condition of human-induced land degradation that occurs in arid, semiarid and dry sub-humid regions (P/PET 0.05 to 0.65) and leads to a persistent decline in economic productivity (>15% of the potential) of useful biota related to a land use or a production system [1-3]. Climatic variations intensify the decline in productivity, restorative management moderates it. Some of the main human and biotic interactions that are causing desertification hazards in the area are:


Introduction
Cultivable land is the valuable natural resource which supports production food and fiber and many other essential goods required to meet human and animal needs for sustenance. However, it is facing serious threats of deterioration due to unrelenting human pressure and utilization incompatible with its capacity. Situation becomes more serious for the nation like India, where to cop up with agriculture production demand, large fertile land is required. A serious threat to this is desertification. Katyal and Vlek describes desertification is a condition of human-induced land degradation that occurs in arid, semiarid and dry sub-humid regions (P/PET 0.05 to 0.65) and leads to a persistent decline in economic productivity (>15% of the potential) of useful biota related to a land use or a production system [1][2][3]. Climatic variations intensify the decline in productivity, restorative management moderates it. Some of the main human and biotic interactions that are causing desertification hazards in the area are: y y Uneconomic land use/cultivation practice on the sand dunes, marginal lands affecting adjacent fertile lands area a means to soil erosion. y y The intensive use of water resources or it's over exploitation leading to rise in water tables, seepage and increased salinity.
The EOT has been proven of immense help in mapping, monitoring and studying change detection of desert areas due to its capacity to cover larger area, temporal data availability, affordable cost and accuracy [4][5][6]. The present study focuses on delineation of major geomorphic features of the area, vulnerable geomorphic processes characterization and identification and GIS analysis for vulnerable classes of desertification.
Rajasthan with four seasons viz., winter, summer, monsoon, and post monsoon. The climate of the region is hot and dry. Rainfall received is very less, the temperature is very high all around the year and all these conditions generate an arid to semi-arid picture of the area. The temperature variations are also great.
The temperature begins to rise from the month of March and May reach up to 50C occasionally particularly in the Barmer district during the June and July. High temperature may be associated with high-speed dust storms, which are normal in the month of April and May. Even in the winter season also the daytime remains quite hot. The received sunshine per day is around 9 hours. This can be given as the reason of high temperature because when sunrays fall on the sand it become hot and raise the surrounding temperature. The mean maximum summer temperatures (may) range from 40°C to 42°C. During winter (December to February) the mean maximum temperature ranges from 15°C to 25°C and the minimum temperature slash down to the freezing point. The average annual rainfall received in the area is about 278.78 mm ( Figure 1).

Spatial Distribution of Land Use/Land Cover
Land use and land cover of the study area is done with ETM 2000 of LANDSAT Satellite data and IRS LISS-III 2006 of all the three-season data viz., Kharif, Rabi and Zaid ( Table 1). The classification scheme adopted for present study includes six classes at level-I and twenty-two classes at level-II. On the basis of land use and land cover area can be broadly classified as agriculture land, built up land, forested land, waste lands and water bodies as per level-1 land use\land cover classification system developed by NRSA. During 2000, about 32.45% area was under fallow land followed by 20.09%, 3.95%, 3.15%, 33.02% area under crop, land with scrub, land without scrub and sandy desertic ( Figure 2). The forest area is very less.

Land degradation assessment
The increasing human and livestock population pressure over   the last decade has disturbed the ecological balance of study area to a considerable extent. As a result, many areas have converted into degraded land. The severity classes find in the area are identified viz., slight, moderate and severe for all wind, water and salinization processes (as per NRC Land Degradation Manual). The major processes of degradation active in the study area are wind erosion, water erosion and salinization. As it falls in the desert, the wind erosion is much more prone then other categories. Area affected by wind erosion process  4.24% of block area is degraded by it, followed by 2.58%, 2.32%, 2.30%, 2.19% and 1.02% areas under Pali, Rohat, Pachpadra, Siwana and Luni blocks respectively. Water erosion is a major process of land degradation both in arable and non-arable lands. However, ravine formation is generally observed in barren lands along river or drainage network due to high intensity rainfall and subsequent rapid runoff. In some of the blocks the moderate and slight water erosion is also observed ( Table 3).
Salinization process (moderate) affected only one or two blocks small area (22413.06 ha) of Pachpadra block, which is 6.52% of the block area and 0.87% (1683.74 ha) area of the luni block. In the part of Siwana slight salinization is also noticed which is 2.17%. Salinization process is active mostly in unirrigated agricultural land and scrublands. Salinity development has been taken place due to inherent limitation or brackish groundwater and its subsequent capillary rise to the surface in the part of Pali and Ahore blocks. In the Pachpadra block one salt basin is also present that is known as Pachpadra salt basin. It covers the total area of 6275.45 ha of the block (1.82%).  (Table 4). Although the change is not that much varied. Changes in the directions namely degraded wasteland categories to cropland, water bodies and plantation etc., has been considered as 'positive change' . About 1032.02 ha have been improved because of 'positive change' . Changes in the reverse direction namely, fallow land to wastelands; forest to wastelands; dry water bodies to wastelands etc. have been considered as 'negative change' . Area degraded due to negative changes covers about 279.31 ha which is almost negligible ( Table 5). Parts of the remaining area have undergone changes but those can't be regarded either positive or negative. About 11832672.84 ha belong to 'no change' category ( Figure 4).

Vulnerability of geomorphic units
The vulnerability of different geomorphic units on the basis of weathering resistant capacity (bearing capacity), water erosion severity, wind erosion severity, vulnerable water erosion classes, vulnerable wind erosion classes with other collateral data like soil erosion, slope etc. is prepared. The classes viz., high, moderate and low are made on this basis. This table shows that dune field, aeolian plain, valley fills, flood plain and piedmont slope aeolian show the high vulnerability to the land degradation and desertification in the particular area of Thar desert. All the geomorphic units consist of igneous rocks shows low to moderate category because of hard and compact nature of the rock and high resistance capacity like-pediment volcanic, pediment granite etc. The geomorphic units like pediment volcanic, denudational hill volcanic show the low category because of their hard and compact nature. Table 6 also shows the reverse relationship between bearing capacity of the rock and vulnerability level. The softer the geomorphic unit, greater the activeness of the erosion activity in the case of wind. In the case of water, it depends upon the chemical reaction. According to the table dune field having the low bearing capacity and thus the vulnerability level is high. In the case of denudational hill volcanic bearing capacity is moderate to good but the vulnerability level is low.