DEFINICIÓN DE SISTEMA DE INFORMACIÓN GEOGRÁFICO (SIG)

Optimal Strategy F3 F4 Ml M2 Total L w a) P p c o o <D W !>■< tn CD P r d U P w F3 F4 Ml M2 Total 5 2 7 7 3 2 1 7 8 3 2 10 2 1

In contrast, of the eight years in which F4 is second-best, for five years F3 turns out to be the optimal strategy. This clearly shows that F4 and F3 are the most desirable strategies overall, with

F4 the single most useful strategy for optimal management of water resources in the small dam.

The consistency of optimality for variations in rainfall adds a further dimension to the generality of our findings.

Insensitivity of the results to slight variation in irrigation policy has been noted already.^ Thus, irrigation or withdrawal

2

strategies which are essentially framed to best supplement

incident rainfall for crop growth are reasonably comparable across policies. Our findings can, therefore, be used to assess the optimality of the strategy actually adopted by the community and this is pursued in the next section.

5.5 Assessment of the Prevalent Practice

It is not possible to comprehensively compare our

irrigation or withdrawal policy with that actually adopted by the community since 1976. The major difficulty, as noted earlier, is the lack of precise data on withdrawals. In fact, we have to rely on our single year's data.

Withdrawals from the dam for the land preparation of the dry season rice cultivation in 1978 and 1979 has been observed to be around the first week of March (Ml). Thus, the prevalent management strategy is inefficient (c.f. (5.1)). This argument can be illustrated by consideration of the hypothetical benefit transformation curve drawn in Figure 2.2 of Chapter 2; for the

1 Recall that an irrigation policy involves the amount of application which in o u t case is constant over time so that different policies would vary only in the level of that constant.

2 Individual irrigation strategies relate to the timing of the first withdrawal to be considered for the dry season.

Ml strategy the value of in situ objective can be increased without any reduction in the level of production of rice. Efficiency can be achieved by moving parallel to the X-axis to the optimal point on the benefit transformation curve which corresponds with advancing the commencement of operations to the last week of February.

To be fair, there can be numerous reasons for this inef­ ficiency in practice. Three obvious possibilities can be listed as follows:

(i) the inability to procure inputs and agricultural credit in time;

(ii) the preference of the community for a longer period of leisure after the harvest of the wet season rice; and (iii) preoccupation with harvesting operations

of slash and b u m agriculture.

However, an earlier study (Mahendrarajah, 1978) shows that the peak harvesting activities of slash and b u m agriculture in the village is in January, preceding the harvesting of wet season rice. Alternatively, difficulties in immediate disposal of this rice to obtain cash and other inputs for dry season cultivation has been observed. This has implications for strengthening the agri-support services to ensure availability of credit and other inputs for

optimal timing of the dry season's cultivation.

Finally, the leisure preference of the community, if significant, will imply a divergence of the technical optimum we have identified

from the economic optimum of the community. In such a situation, a larger leisure utility and hence a delayed commencement of the dry

season cultivation has to be compensated by a forfeit of some in situ benefits owing to the accompanying reduction of water storage in the dam. An alternative possibility is to reduce the extent of

cultivation retaining the same level of in situ benefits. The third is a combination of these two. However, leisure preference and related aspects are not pursued in this dissertation.

5.6 Summary of Results

The results presented in this chapter could be summarised as follows:

(i) The minimal supplementary irrigation policy designed ensures at least a minimum

application level of 0.5 acre inch per week over a period of 11 weeks. The

definition of decision rules were heuristic and drew heavily on the author's field observations.

(ii) For implementing the policy, altogether ten strategies were examined individually in the simulation framework provided in Chapter 4. The simulation model was based on the rainfall and storage data for the year 1976/77 which was also used earlier in the identification of the time series model. The choice of the optimal strategy was aided by three criteria: the amount of withdrawal, mean storage at the end of the dry season and the probability of emptying the dam.

The F4 and F3 strategies turned out to be optimal and second best respectively. (iv) There appeared to be no advantage in

commencing dry season cultivation earlier than the third week of February.

(v) The prevalent practice or strategy of withdrawal, that is, commencing the dry

season rice cultivation in the first week of March, is clearly not optimal for the optimality criteria and within the choice space considered here.

CHAPTER 6