Minimizing irrigation water demand: An evaluation of shifting planting dates in Sri Lanka

Abstract

Climate change coupled with increasing demands for water necessitates an improved understanding of the water-food nexus at a scale local enough to inform farmer adaptations. Such assessments are particularly important for nations with significant small-scale farming and high spatial variability in climate, such as Sri Lanka. By comparing historical patterns of irrigation water requirements (IWRs) to rice planting records, we estimate that shifting rice planting dates to earlier in the season could yield water savings of up to 6%. Our findings demonstrate the potential of low-cost adaptation strategies to help meet crop production demands in water-scarce environments. This local-scale assessment of IWRs in Sri Lanka highlights the value of using historical data to inform agricultural management of water resources when high-skilled forecasts are not available. Given national policies prioritizing in-country production and farmers' sensitivities to water stress, decision-makers should consider local degrees of climate variability in institutional design of irrigation management structures.

Keywords: Climate change adaptation; Crop production; Food security; Irrigation water requirements; Planting dates; Water resources management.

Fig. 1

Climate zones and location of the four stations

Fig. 2

Distribution of seasonal irrigation water requirements (X _i,j from Eq. 5) at the four study locations

Fig. 3

Intraseasonal coefficient of variation in irrigation water requirements (C _V,j from Eq. 7; black points) compared to interseasonal coefficient of variation at each station (C _V from Eq. 6; red-dotted lines)

Fig. 4

Average seasonal irrigation water requirements (${\overline{X}}_j$. from Eq. 5; black solid lines) fitted with a linear model fit (blue-dotted lines) and corresponding 95% confidence interval (gray-shaded areas). None of the slopes is significantly different from zero (p > 0.05 for all)

Fig. 5

Seasonal irrigation water requirements as a function of planting date (X _i,j from Eq. 5) at Maha Iluppallama (points in gray are lower than that season’s 25th percentile while points in black are greater than or equal to the 25th percentile). Vertical green line indicates actual date rice was planted; rice was not planted in the irrigation area near the Kalawewa tank during 2006

Fig. 6

Potential average water savings in irrigation water requirements as a function of planting date (W _S,k from Eq. 8)