عنوان مقاله [English]
The current situation of water resources in Iran, the trend and trends governing it, as well as considering the inappropriate spatial and temporal distribution of water per capita and its excessive consumption, show the necessity of demand management. In this regard, improving the efficiency of water consumption, especially in the agricultural sector, is considered as an opportunity to save more water. Optimum water management requires a great change and to ensure the sustainability of these resources, integrated and systematic management should be applied in line with optimal processing and exploitation with the application of new technology for maximum utilization of these resources in planning. Improving the efficiency of water consumption has been introduced as one of the most important ways to reduce water consumption, but it can be seen that the aforementioned improvement does not necessarily reduce water consumption to the saved amount and sometimes leads to no change or even an increase in water consumption. only the use of new and efficient irrigation methods cannot be effective in adjusting the consumption and balancing the supply and demand of water. In explaining why water consumption has not decreased despite the large investment in the field of modern irrigation technology, the concept previously expressed in the field of energy consumption, i.e. the rebound effect, can be useful. The rebound effect, which is more prominent in the literature of energy economy, in the field of water, can be considered a mechanism that causes a part of the water saved due to the improvement of water efficiency to be reused and, as a result, leads to a reduction in the amount of water saved. In simpler terms, the return effect can be defined as a percentage of the potential water savings resulting from water efficiency improvement, which reflects the difference between the potential and actual savings in water consumption. The return effect is usually defined in relation to different forms of energy, such as fuel or electricity, but in this research, an attempt is made to investigate the return effect for agricultural water.
the price of agricultural water is determined by the government in most countries according to the nature of agricultural goods and its importance for the society and is kept almost constant. Therefore, the price elasticity method is not a suitable method to estimate the return effect of agricultural water. According to these materials, in this research, the direct comparison method has been used to estimate the effect of agricultural water return at the macroeconomic level. In equation 1, the estimation of the return effect requires the estimation of the expected water storage (EWS) resulting from the increase in efficiency and the estimation of the return water used (RWU) resulting from the reduction of water cost. The relationship between water consumption and partial water productivity can be considered as follows: W="Y" /"WP"
In which, W represents total agricultural water consumption, Y represents total agricultural production, and WP represents agricultural water productivity at the macroeconomic level. If it is assumed that agricultural water consumption, agricultural production and water productivity in year t are W_t, Y_t and WPt, respectively. According to the equation, the change in agricultural water consumption from year t-1 to year t is represented by (∆w_t), which can be decomposed as follows
∆wt = Wt- W (t-1) = Yt/(WPt ) - Y (t-1)/(WP (t-1) ) = (Yt ∆WPt)/(WPt WP (t-1) ) + (∆Yt)/( WPt-1)
According to this equation, the change in agricultural water consumption (∆wt) can be divided into two parts: the change in agricultural water consumption due to the change in water productivity ((Yt ∆WPt)/(WPt WP (t-1) )) and the change to The reason for the growth of agricultural production ((∆Yt)/(WP (t-1) )). Changes in agricultural water use in addition to growth in agricultural production can be due to technological progress. ρ is assumed to be the rate of change due to technological advances. Therefore, return water use (RWU), which represents the return (or surplus) of water as a result of increasing water productivity, is equal to (ρ∆Yt)/(WP (t-1)) and EWS, which represents the expected water savings ( calculated or predicted) after increasing irrigation efficiency is equal to (Yt ∆WPt)/(WPt WP (t-1)). It can be concluded that the formula for the return effects of water in year t is:
WRE=(∑ (ρ∆Yt)/(WP (t-1) ) )⁄(∑ (Yt ∆WPt)/(WPt WP (t-1) ) )×100
According to the above equation, the return effect of water is the increase in the ratio of water consumption due to the growth of agricultural production to the reduction of the expected water reserve through the improvement of water efficiency. Here, both the improvement of water productivity and the growth of agricultural production are created by methods of improving irrigation efficiency. Based on equation 6, another important factor in estimating the return effect is to estimate the exact contribution of technological progress (ρ). For this purpose, according to the production function of Cobb Douglas Hicks-Neutral, which is as follows :
"Y" _"it" "=" "A" _"it" 〖" W" 〗_"it" ^"α " "X" _"1it" ^"β" " " "X" _"2it " ^"γ" … X_nit^ω=A_i e^rt 〖 W〗_it^(α ) X_1it^β " " "X" _"2it " ^"γ" … "X" _"nit" ^"ω"
By taking the logarithm from the above equation, we can reach equation:
Ln"Y" _"it" =ln A_i+rt+ α ln"W" _"it" +β lnX_1it+γ lnX_2it+…+ ωlnX_nit
In this way, by using the estimation of this equation based on the provincial data during the studied period, the r coefficient can be extracted.
Now the participation rate of technological progress (ρ) can be calculated as follows:
r: represents the growth rate of technology and (gy) represents the growth rate of agricultural production. Finally, by using equation, the effects of agricultural water return can be calculated at the macroeconomic level and in the agricultural sector.
The return effect of agricultural water in Kurdistan province was 106.25%, which has the highest return effect during the studied period. And the second rank belongs to Bushehr province with a rate of 91.19%, the lowest rate of return effect is for East Azarbaijan, Golestan and Tehran provinces (1.45), (2.63) and (3.50) respectively. The return effect is greater than 100% only in Kurdistan Province by 106.25%, these results show that measures to improve water efficiency in Kurdistan Province can increase agricultural water consumption in this province, which is the phenomenon of "Jones' Paradox".
In some cases, the amount of return effect is negative, in other words, the measures taken to improve the efficiency of the new irrigation system have caused the predicted water savings to exceed the actual amount of water savings. It should be noted that, theoretically, this phenomenon is only It occurs in the case of a decrease in the production of agricultural products. Therefore, in the provinces where the return effect is negative, according to the data used, the amount of agricultural production in the desired year was less than the previous year, or the water productivity in year t was less than year t-1, this situation can be due to the change in water conditions and The country's weather, such as drought or extreme cold, and the decrease in agricultural production compared to the previous year, or due to the country's structural changes from agriculture to industrial mode.
The results show that a partial rebound effect is evident in Iran in the studied years. Water savings have not fully met expectations and some of the expected water savings have been reused. It can be seen that the highest return effect is in 2018 and also in 2013 it has experienced a negative return effect, the negative return effect indicates the existence of savings in this period, but as it was said, this result can be affected by the reduction of agricultural production due to changes in the use of agricultural water, so the negative return effect alone is not a reason that the water efficiency improvement system is affected, in addition, the lowest return effect is in 2013, which is 11%, which shows that 89% of the stored water and only 11% of it is used again. So, in fact, the annual return effect is sensitive to changes in agricultural water use and depends to some extent on natural factors, such as rainfall. In general, the findings indicate that the agricultural water savings due to the improvement of irrigation system efficiency has been reduced by 15.29% due to the increase in demand for irrigation. In fact, this largely shows the success of the policy of increasing water efficiency in order to reduce water consumption.
The results of the findings showed that during the studied period, the return effect for Iran was on average 15%, which indicates that about 15% of the water saved due to the increase in agricultural water efficiency was reused in this sector. In other words, about 85% of water has been saved, which somehow shows that the policy of increasing agricultural irrigation efficiency can have positive effects on Iran's water reserves in the long run.