Effect of scale on water users’ associations’ performance in Tunisia: nonparametric model for scale elasticity calculation

The paper aims to investigate the economies of scale of Water Users’ Associations (WUA) inTunisia. During the last years there has been a lot of discussion in Tunisia about the optimal sizeof WUAs, which allows more efficient management of the water resources at the local level. Inthis work we propose to see if the size of the WUA in the governorate of Nabeul (Central-Easternpart of Tunisia) would have to increase or decrease in order to maximize their efficiency. Apartfrom this qualification we also quantify the scale efficiency and scale elasticity of the WUA usingData Envelopment Analysis (DEA) models. The results show that the output space (volume ofwater distributed and number of ha managed and irrigated) of the WUA that attain a high level ofscale efficiency is highly diverse, indicating that the number of ha irrigated and the volume ofwater distributed are not explaining the differences in the scale efficiency of WUA. Thecalculation of scale elasticity of the WUA shows that 41% of the WUA are operating atdecreasing returns to scale (DRS) while 16% and 43% operate at constant (CRS) and increasing(IRS) returns to scale, respectively. The scale orientation was found to be depending on theoutput density rather than on the output size. Thus, WUA located in more irrigation-intensifiedareas were found to be IRS oriented. WUA operating at CRS were found to have the minimumcosts, which is in line with the theoretical predictions that suggest that the average productivity ismaximized when the scale efficiency is equal to 1.