Effect of progressive irrigation development on the environment: a case study of North - Bangladesh

Abstract

lnl3anglade,h, lhe groundwater irrigation development starled in lhc 1960s and ;ince then it has been increasing progressively especially in the Northern region. At presellt, irrigation covers almost all the agricullural land in the region during dry period that provide, as a source for potential evapo-transpir"tion. In this study, an auempt has been made to analyze the impacts of progressive inigation developmenl on ellmatic parameters, land use, cropping pattern and soil fertility. This study is mostly based on secondary data and inrormation. Data or greater Rangpur, greater Dinajpur and Patuakhali on daily maximum tempemlure, minimum temperature, relative humidity, evaporation and irrigated area were used. Ranb'Pur and Dinajpllf with extensive developmenl in irrigation were considcred as the study area and Patuakhali with very little ilTigalion was considered as the control area. Data on soil fertility and cropping pattern were also analyzed wilh rclation to irrigaled arca, In case of wil fertility, the analy~is was performed only within the study area. The results of the analy~i5 reveal that during the irrigation season (January-April), the maximum temperature is deercasing in Rangpur and Dinajpur at a rale of 0.5°(" and 0.46"C per decade respeetivcly, ln Patuakhali, the maximum temperalure is increasing at a rate of 0.237oC per dceadc. rhe minimum temgcrature is increasing over the years in Rangpm and Dinajpur at a rate ofO.5GC and 0.27 C pcr decade but in case of Patuakhali, il docs not sho\\' any definitc trend. Although, lhe evaporation is supposed to have increased over time with Lhe increase in irrigated area but it has been observed that the rate of evaporation i; decreasing over time at a rate of 0,038 mill and 0.507 mm per decade in Rangpur and Dinajpur respectively. II has also beell found lhal the relative humidity is increasing over the years at a ratc of 0.137% and 1.275% per decade in Rangpur and Dinajpur re~pecljvely. The relative humidity of Patuakhali does not show allY definite lrend. Thc study has abo revealed that there ;, a positive relationship between irrigation development and cropping pattern changes. Mostly 13oro rice is being cultivated with lhc developmenl of irrigation. Cropping intensity in Ranb'Pur, Dinajpur and in Patuakhali in the pre'ient dccade is 227%, 212% and 200% respectively. The carbon contcnt in the 0-15 em soil layer mostly increa,ed in the study area. The study arca experiences a ,harp fall in the total nilrogen content which may be due to the changes in cmpping sy,tems. All the physiographic units showed a decline in the content of exchange.1ble pota%ium except for greater Dinajpur. Changes in the phosphorus availabilily in the study area are mixed. From the FGDs, it ha~ been observed that there is .1 perception lhal the maximum temperature is decrea,ing. The dryness of weather has also been reduced. Soil fertility ha<; bccn ['educed as lhe land is being cultivaled continuously with the advcnt of irrigation. The findings of the stlldy suggest that the progressive development of irrigation in the last fort}' yeur$ has no adverse impact on the climatic parnmeters except that it ha$ reduced the diurnal variation of temperature in the Irrigated areas, As the irrigatioll is directly related with cropping paltern and hence with the soil fcrtility so the cropping pattern has 10 bc chosen carefully to avoid any adverse impact on soil fertility.