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Remote Sensing based rapid watershed health appraisal – a case study of NWDPRA watersheds of Rajasthan
Vegetation vigour:
Percent distribution of various vigour types is given in Table 7 and 8. Significant increase in the moderate and good vigour (NDVI) is apparent in w2 and w5, whereas significant decrease in both these types is noticed in w3 and w4. The decrease in the moderate to very good vigour in agricultural watersheds (w1, w3, w8) could be due to crop harvesting or more area kept under fallow. Whereas in forested watershed (w6) the decrease in good and very good type is due to degradation of forest and/or the deficient rainfall year in 1996. Among the wasteland watersheds only w4 has got deterioration in vegetative cover, however, w2 and w7 exhibits better vigour condition. Overall observation indicates that for 5 watersheds (w1, s2, w5, w6 and w8) the dominant category has remained same for both the years (Fig. 4 and Table 9) but in w3 and w4 the moderate vigour type is changed to poor, whereas as a sign of little improvement in w7, the dominant types change to poor from very poor.
Table 8: Percent distribution of vegetation vigour types in 1996
 Fig. 4: Percent changes in vegetation vigour between 1988 and 1996 Table 9: Percent changes in vegetation vigour types between 1988 and 1996
Drainage line performance In desert regions most of the streams are eroded and devoid of any vegetation. As the soil is mostly sandy with poor moisture retention capacity, following storm incidence run-off water flows with a very high kinetic energy, resulting in bank erosion and sediment transport. With every storm incidence these drains bulges in their dimension and turns to deep gullies. Any conservation measure to stabilize these gullied lands would be manifested through better moisture retention in the gully beds and surrounding zones. Due to moisture retention and sediment deposition good vegetation comes up in due course of time and helps in reducing the impact of rain drop, providing safer velocity of flood water through the channels and helps in better soil and water conservation. Keeping these in view, a buffer mask of the drainage lines with 50 m either side was created to glance through the buffer window what is the vegetation status at various level of drainage line treatment. Different vigour types and their relative distribution are given in Table 8 and 9 for the year 1988 and 1996 respectively.
Table 11: Vegetation vigour along drainage buffer in 1996
Comparative study of two years performance of the watersheds reveals that the condition of vegetation around the streams/drains are improved in w1, w6, w7 and w8 (Fig. 5 and Table 12). In all these watersheds the proportion of moderate, good and very good types have increased substantially and contributes 6.59%, 12.69%, 1.08% and 10.55% respectively. There is also a decrease in poor or very poor type over the years. This have been possible due to better moisture availability, along drain vegetation which comes up naturally due to favourable soil hydrology. Although the development is slow but is stable. However, significant decrease in vigour type is observable in w2, w3, w4 and w5. There is a very large decrease in moderate to good vegetation type due to anthropogenic activities and the decrease accounted to be 23.16%, 26.31%, 13.49% and 31.81% respectively. The proportion of decrease is more than the increase in vigour. Annual rainfall distribution in the watersheds (district average) indicates that annual rainfall was higher in 1996 than 1988 for w1, w2, w3, w4, w5 and w8 whereas less rainfall was recorded in w6 and w7. Hence out of eight, 4 watersheds (w1, w6, w7 and w8) performed well in terms of drainage line stabilization. In w6 and w7 the vigour was found to be better even if the rainfall was less in 1996 than 1988. For w2, w3, w4 and w5 the major reason for poor performance could be due to less rainfall year. 
Fig. 4: Percent changes in vegetation vigour along drain between 1988 and 1996 Table 12: Percent changes in vegetation vigour along drain between 1988 and 1996
Composite ranking for RSWHI Table 13 represents the composite average weight received by different watersheds. These indicators give overall relative performance during 1996 over the base year 1988. The relative ranking is also given in Table 13 separately for landuse, overall biomass and biomass along the drainage line. Individual ranking wise Ambali performed best both in terms of landuse and biomass change. Broadly the rank remained same for Ambali, Syala and Kharkhadi in terms of landuse but better performance is noticeable in Kamli and Kheri. Ambali, Kheri, Syala and Mewanagar remained same in terms of ranking for overall watershed vegetation status. Improvement in rank is found in Bawliya pada, and Kharkhadi. Drainage line vegetation is an important indicator for the erosion control measures and in the present study improvement is found in Ambali, Kharkhadi Kheri and Syala. However the rank remained the same for Mewanagar. Marginal negative performance in landuse practice was found in Bawliya pada and Bhirathai Kalan.
To analyse the overall performance of the watersheds in terms of landuse, vegetation vigour and drainage line vegetation density all the individual index values were summed and averaged (Fig. 5 and Table 14) to better represent the effect of watershed treatment. In developing such composite index the values less than 1 indicate negative performance and more than 1 indicates positive performance. In the present study 5 watersheds showed overall positive performance in health and three showed negative health performance. The degree of positive change in higher only in Mewanagar but for rest 4 the performance is only marginally improved and remained almost unchanged. The watersheds showed negative performance include Bhirathai kalan, Kamli, and Syala. However in Syala and Kamli the performance is marginally negative where as in Birathai kalan it is considerable. Hence from this study it can be concluded that only watershed showed good performance is Mewanagar having located in arid western plain and the poor performance was found in Birathai kalan, which is largely attributed to large area devoid of vegetation.  Fig. 5: Watershed health index and composite ranking Table 14: Watershed health index and composite ranking
Conclusion Eight watersheds distributed across different agro climatic zones of Rajasthan were studied for rapid appraisal of their health condition after 8 years of treatment. Major remote sensing based indicators studied include landuse, overall biomass, vegetation along drainage buffer zone and number and extent of water body. Distribution of landuse, and biomass have been analysed and their change over the years have also been calculated. For comparative performance evaluation area weighted spatial averaging of the landuse and vegetation index were performed and ranked accordingly. Finally the ratio of the weighted spatial average values of landuse and vegetation index was calculated for all the watersheds. Positive change was noticed from all the watersheds except one for landuse, whereas only 4 watersheds showed positive change in terms of biomass development. The biomass especially the ephemerals are highly dynamic as a function of rainfall amount and distribution and hence more precisely the vegetation along the drainage line was analysed which could be used as an indicator due to impact of drainage line treatment. Only 4 watersheds had good biomass along the drainage buffer zone and rest had negative. All of them showed better performance in comparison to overall biomass of the watershed. All the weighted values were finally averaged to derive the RSWHI and ranked accordingly. Mewanagar watershed performed the best among 8 but Birathai kalan, Kamli and Syala performed poorly. Acknowledgements The authors are thankful to RFD, Ministry of Agriculture for giving opportunity to carry out the study. Thanks are also due to the staff members of RRSSCJ for their kind help and assistance during the course of investigation. References
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