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Reference Crop Evapotranspiration Under Changing Climate in North-west Hydrological Region of Bangladesh

RAHENA PARVIN RANNU
MASTER OF SCIENCE (AGRICULTURAL ENGINEERING) IN IRRIGATION AND WATER MANAGEMENT, DEPARTMENT OF IRRIGATION AND WATER MANAGEMENT, BANGLADESH AGRICULTURAL UNIVERSITY, MYMENSINGH-2202 Examination Roll No. 11 IWM JD 08 M, Registration No. 33621, Session:2006-2007, Semester: July-December 2012

Abstract/ Executive Summary:

Climate change is one of the most important global environmental challenges facing humanity with implications for food production, natural ecosystem and water supply. The expected climate change is thought to have severe impacts on agriculture, hydrological stem, ecosystem and other related systems. Reference crop evapotranspiration (ET₀), which is a measure of atmospheric evaporative demand, is independent of crop type, crop development and management practices. It provides a measure of the integrated effect of radiation, wind, temperature and humidity and its variability is affected by these climatic parameters. The information in these regard in Bangladesh is however lacking. So, this study identified the climatic parameters that are responsible for the variability of ET₀ in Dinajpur and Bogra districts of the North-West Hydrological region of Bangladesh. Daily climatic parameters for a period of 21 years (1990-2010) of these districts were collected from the Bangladesh Meteorological Department. ET₀ was determined by FAO Penman-Monteith method. Trend analysis of each parameter of ET 0 was done by MAKESENS trend model and correlation between ET₀ and its controlling parameters were analysed. The results showed a decreasing trend of ET₀ over most of the period of the year in Dinajpur and Bogra districts. A single or different combinations of ETo determining parameters was/were responsible for the decreasing rate of ET₀ in different decades of the months and months of the year. The responsible parameters that caused variation in ET₀ differed in different decades and months. A decreasing rate of net radiation, saturation vapour pressure deficit and wind speed only in Dinajpur district, and net radiation and wind speed in Bogra district played the dominant roles for the decreasing rate of ET₀ under changing climatic condition. This study thus provides basic information on the variability of reference crop evapotranspiration due to climate change. This information can be used for water resources management and planning in irrigated agriculture of the North-West Hydrological region of Bangladesh. area. Vulnerabilities to water-related disasters are predominantly due to acute climate variability and extreme events, which are manifested by both spatial and temporal distribution of water resources available throughout the region. The soil in this region is mostly reddish and hard. Drought commonly occurs here since the rivers dry out in the dry season. On the other hand, it is very frequently affected by floods in monsoon. The changes in the physical system of this region include (a) crop agriculture, (b) livestock production, (c) aquaculture and fish production, (d) forest and vegetation and (e) livelihoods of poor and marginal households. Due to changes in temperature and humidity, human health will also be affected. The high susceptibility to water-based natural hazards will affect settlement of the population and also immobile physical infrastructure. To effectively manage the nation's water resources, water managers need to understand the significance of evapotranspiration in the hydrologic budget. The information on any change of ETo and climatic mechanism related to its variability due to climate change in Bangladesh is still lacking.

Keywords: Reference crop ET, Changing climate, North-west hydrological region

Location: Dinajpur and Bogra districts

Start Date: 00-01-1990

End Date: 00-12-2010

Program Area: Risk Management in Agriculture

Non-commodity: Adoption and mitigation technology

Objectives:

1.To detect the trend of governing factors of reference crop evapotranspiration in North-West hydrological region of Bangladesh, 2.To detect and estimate the trend of reference crop evapotranspiration under changing climate in the region, and 3.To identify the responsible parameters that cause variability m the reference crop evapotranspiration.

Methodology:

Daily climatic parameters like maximum temperature, minimum temperature, maximum relative humidity, minimum relative humidity, wind speed and sunshine duration of Dinajpur and Bogra districts for a period of 21 years (1990-2010) were collected from the Bangladesh Meteorological Department, Dhaka, Bangladesh. The daily agro-climatic parameters were arranged in mean decade-wise and mean monthly-wise. Some of the climatic parameters were found partially missing. The missing data were computed by simple arithmetic average of the index stations. A large number of empirical or semi-empirical methods have been developed for assessing reference crop evapotranspiration, ET₀, from climatic parameters. Some of the methods are only valid under specific climatic conditions and cannot be applied under different conditions from those for which they were originally developed. Numerous researchers have analyzed the performance of various calculation methods for different locations. The performance analysis of the various methods reveals the need for formulating a standard method for the computation of ETo. As a result of an Expert Consultation held in May 1990, in collaboration with the International Commission for Irrigation and Drainage and World Meteorological Organization, the panel of experts defmed the reference crop as a hypothetical crop with an assumed crop height of 0.12 m having a surface resistance of 70 sm^-1 and albedo of 0.23, closely resembling the evaporation of an extension surface of green grass of uniform height which is actively growing and adequately watered. The panel recommended the FAO Penman-Monteith method as a standard method for definition and determination of ETo. So, this method has been selected in this study. Daily maximum temperature, minimum temperature, maximum relative humidity, minimum relative humidity wind speed and sunshine duration were used for determination of different parameters and constants of ETo. The equations for calculation of different parameters and constants of ET₀ by the FAO Penman-Monteith method has been used.

Source of Information: MASTER OF SCIENCE (AGRICULTURAL ENGINEERING) IN IRRIGATION AND WATER MANAGEMENT, DEPARTMENT OF IRRIGATION AND WATER MANAGEMENT, BANGLADESH AGRICULTURAL UNIVERSITY, MYMENSINGH-2202 Examination Roll No. 11 IWM JD 08 M, Registration No. 33621, Session:2006-2007, Semester: July-December 2012

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

1. The govermng parameters of reference crop evapotranspiration, ET₀, changed consistently, both temporally and regionally, due to changes of climate in Dinajpur and Bogra districts. The rate of change (increase or decrease) of the governing parameters of ET₀ differed at different times (decades and months) in both districts. 2. ETo decreased, most cases significantly, over most of the times in January, February, March, April, June, August, November and December in Dinajpur district. It decreased over most times in January, March, April, June, August, October and December in Bogra district. 3. Responsible ETo determining parameters were net radiation, saturation vapour pressure deficit and wind speed in Dinajpur district, and net radiation and wind speed only in Bogra district. These parameters played important roles for the decreasing rate of reference crop evapotranspiration.

Knowledge Management: Thesis