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Impact of Climatic Parameters on Reference Crop Evapotranspiration in Sylhet District of Bangladesh

Md. Abdul Kader
MS Thesis, Department of Irrigation and Water Management, Bangladesh Agricultural University, Mymensingh Roll No. 13 IWM JJ 02 M, Registration No.: 34578, Session: 2007-2008

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. Reference crop evapotranspiration (ET_a) is an important part of water cycle in agricultural ecosystem, which has a distinct effect on crop growth and yield. The implications of climate change on ET_a are of high importance for agriculture regarding water management and irrigation scheduling. The aim of this study was to analyze variations of climate and its effect on ET_a in Sylhet district of Bangladesh over the period from 1981 to 2010. For this purpose, data of daily climatic parameters (temperature, humidity, wind speed and sunshine duration) were collected from the Bangladesh Meteorological Department. FAO Penman-Monteith method was applied for determining ET_a from the climatic parameters. Trend analysis of each climatic parameter used for determining ET_a was done by MAKESENS trend model, and correlations between ET_a and its controlling parameters were analyzed. The results showed an increasing trend of ET_a over most of the period of year in Sylhet district. A single and/ or different combinations of ET_a determining parameters was/were found responsible for the increasing rate of ET_a in different decades of the months and months of the year. The responsible parameters that caused variation in ET_a differed in different decades and months. An increasing trend of average temperature, net radiation and saturation vapour pressure deficit played the most dominant roles for the increasing rate of ET_a under changing climatic condition. This study thus provides basic information on the variability of reference crop evapotranspiration due to climate change in the study area. This information can be used for water resources management and planning irrigated agriculture of the Sylhet district of Bangladesh.

Keywords: Impact, climate parameters, reference ET crop, Sylhet

Location: Khasia-Iainta hills of India on the north, Maulvi Bazar district on the south, Kachhar and Karimganj districts of India on the east, Sunamganj and Habiganj districts on the west.

Start Date: 00-01-1981

End Date: 00-12-2010

Program Area: Risk Management in Agriculture

Non-commodity: Management

Objectives:

1. To detect trend of governing factors of reference crop evapotranspiration in Sylhet district of Bangladesh, 2. To detect and estimate trend of reference crop evapotranspiration under changing climate in Sylhet district, and 3. To identify responsible parameters that cause variability in reference crop evapotranspiration.

Methodology:

There are eight Hydrological Regions in Bangladesh: North West (NW), North Central (NC), North East (NE), South East (SE), South Central (SC), South West (SW), Eastern Hills (EH), and the active floodplains and charlands of the main rivers and estuaries. The NE Hydrological Region comprised 7 districts of which Sylhet district was selected for this study. Sylhet district is situated within 24°36"-25°11" North latitude and 91°38"-92°30" East longitude. This district, with an area of 3,452.07 km, is bounded by the Khasia-Iainta hills of India on the north, Maulvi Bazar district on the south, Kachhar and Karimganj districts of India on the east, Sunamganj and Habiganj districts on the west. The city is within the monsoon climatic zone, with annual average highest temperature of 33.20°C and the lowest of 13.60°C. Nearly 80% of the annual average rainfall of 3,334 mm occurs between May and September. Main rivers in this district are the Surma, Kushiara, piaen and Sharee. There are 82 haors and beels in Sylhet. Shingua Beel (12.65 sq. km) and Chatla Beel (11.86 sq km) are notable. The climate of Sylhet is humid sub-tropical with a predominantly hot and humid summer, and a relatively cool winter. Main occupations in this district are agriculture (30.82% ).The main crops are paddy, mustard, betel and nut, and the main fruits are mango, jackfruit, orange and litchi. Daily climatic parameters like maximum and minimum temperatures, maximum and minimum relative humidity, wind speed and sunshine duration of Sylhet district for a period of 30 years (1981-2010) were collected from the Bangladesh Meteorologial Department. 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 lor 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 defined 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 ET. 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 ET_o. The equations for calculation of different parameters and constants of ET₀ by the FAO Penman-Monteith method have been used.

Source of Information: MS Thesis, Department of Irrigation and Water Management, Bangladesh Agricultural University, Mymensingh Roll No. 13 IWM JJ 02 M, Registration No.: 34578, Session: 2007-2008

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The major conclusions, in light of this study, have been drawn. (i) The governing parameters of reference crop evapotranspiration, ET_a, changed temporally due to changes of climate. The rate of change (increase or decrease) of the governing parameters of ET_a differed at different times (decades and months). (ii) ET_a increased, in most cases significantly, over most of the times in February, March, July and September. (iii) Responsible ET_a-determining parameters were temperature, net radiation and saturation vapour pressure deficit. These parameters played important roles for the increasing rate of reference crop evapotranspiration.

Knowledge Management: Thesis