The Impact of Physiography and Weather Abnormalities on ... · PDF file2 Sherubtse College, Royal University of Bhutan, Kanglung, Bhutan Abstract Rice is the staple food for a majority

Occasional Publication No. 1, September 2015 Centre for Rural Development Studies, College of Natural Resources, Lobesa, Royal University of Bhutan

23 Proceedings of the Conference on ‘Climate Change, Environment and Development in Bhutan’

2-3 April, 2015, Royal University of Bhutan (RUB), Thimphu, Bhutan Editors: Shahnawaz and Ugyen Thinley

The Impact of Physiography and Weather Abnormalities on Rice Yield A Case Study of Paro Dzongkhag, Bhutan

Tenzin1 and Pankaj Thapa2

1 Gross National Happiness Commission, Royal Government of Bhutan, Thimphu Correspondence: [email protected]

2 Sherubtse College, Royal University of Bhutan, Kanglung, Bhutan

Abstract Rice is the staple food for a majority of the people in Bhutan. Paro Dzongkhag (district) contributes the second largest production of rice in the country. Government records indicate that the yield of rice has decreased during the recent years. Among all other factors, the abnormalities in weather conditions are considered as the most dominant cause for declining rice yield especially in the rain-fed cultivation. The present study analyses the impact of variability in precipitation and tempera-tures on the rice yield in two micro climatic zones in Paro Dzongkhag. The meteorological data of six years and the rice yield during the same years, along with the impact of elevation (agro-ecological zone) and slope, were analysed. The results reveal a high positive correlation between precipitation and rice yield in the elevation zone of 2400 to 2600 m and low negative correlation in the elevation below 2400 m. Abnormalities in rainfall have a negative impact on the yield of rice on rainfed cultivation which occupies a significant proportion of the agricultural land in Bhutan. The case study reveals a strong influence of geographical factors on the yield of rice even within two closely spaced micro-climatic zones. In the wake of climate change, it is preferable to analyse im-pacts at micro levels for highly diverse physiographical regions in Bhutan, rather than generalizing it at larger scales. Such approaches can help better understand, plan and prepare for agricultural de-velopment to adapt to the serious challenges likely to be posed by climate change. Keywords: Agriculture in Bhutan, impact of climate, geospatial techniques, micro-climatic zones, rice yield, weather abnormalities.

Introduction

The Inter-governmental Panel on Climate Change (IPCC, 2001) projects a rise of 1.4oC to 5.8oC in the global mean of near surface air temperatures between 1990 and 2100, which will lead to an increase in the water requirements of various crops. The negative impact of climate change on paddy cultivation in different geographical regions has also been reported by various researchers (Shah et al, 2011; Sahid, 2011; Toriman et al, 2013). Similar studies conducted in the Nepal Himalayas indicate a significant non-linear relationship between maximum daily tempera-tures and yield of rice, which tends to decline if the temperatures exceed the critical limit of 29.9°C (Karn, 2014). Precipitation also has a negative effect on the rice yield if higher rainfall is received during its nursery or harvesting stages.

Bhutan is largely an agrarian economy engaging about 69 percent workforce in agriculture

and livestock farming. Rice is the second major crop, after maize, cultivated in the country and Paro Dzongkhag (District) is the second largest producer of this food grain. The adverse impacts of climatic variations on the agricultural activities have been observed in the neighbouring part of the Himalayas. Such impacts are expected to have serious consequences for rice cultivation in Bhutan. The farmers in the country largely follow traditional agricultural practices. Only a small proportion of the farmers has adopted modern agricultural inputs i.e. chemical fertilizer are used by 33 percent, plant protection chemicals by 16 percent and power tillers by 10 percent farmers




only (Minten and Dukpa, 2010). The prevailing spatial differences in agricultural practices and technological adoption, mainly due to infrastructural or institutional deficiencies, are expected to worsen further due to the effects of weather abnormalities.

The Royal Government of Bhutan has formulated certain policies aiming at sustainable agri-

cultural development through integrated cropping system. The target of the country is to achieve at least 70 percent self-sufficiency in food grain consumption and increasing the production of high value low volume cash crops (Tobgay, 2005). Study Area

Paro Dzongkhag is well recognised for the production of high quality Bhutanese red rice. It is located in the western part of the country (Map 1) and its total geographical area is 1287 km2. It has 10 Gewogs (sub-districts) namely Tsento, Doteng, Lamgong, Dobshari, Wangchang, Hoon-grel, Loong-nyi, Sharpa, Dokar and Nagya. It lies in the temperate agro-climatic zone (MOAF, 2011) with the elevation ranging from 2000 to 3000 m. The mean temperatures vary between 5˚C to 8˚C during winters and between 10˚C to 22˚C during summers. The total annual rainfall varies between 1500 and 2000 mm. A larger proportion of the rainfall is received during the monsoon season between June and September. The nursery and plantation period of rice in Bhu-tan is from March to May, growth period from June to August and harvesting time in September-October. Since the monsoon season is also the growth period of rice so the amount of rainfall during these months plays a significant role in the yield of rice.

Map 1. Location of Paro Dzongkhag and its Ten Gewogs




Materials and Methods This study is based on three types of data sets i.e. physiographic, climatic and land use land

cover (LULC). The physiographic parameters, i.e. elevation and slope, were derived from AS-TER GDEM of 30 m spatial resolution. The precipitation and temperature data recorded at two meteorological station located in the study area, i.e. Drugyel Dzong and Paro DSC, were ob-tained from the Department of Hydromet Services, Ministry of Economic Affairs, Royal Gov-ernment of Bhutan (MoEA). The data on LULC of 2010 as well as the rice, production and yield of rice cultivation was collected from the Ministry of Agriculture and Forests (MoAF, 2011).

The minimum elevation in Paro Dzongkhag is about 1900 m and maximum is little higher than 5600 m. The boundaries of the study area cut across three agro-ecological Zones (NSB, 2014, p.17) i.e. warm temperate, cool temperate and alpine zones. In the present study, the warm temperate zone has been sub-divided into warm temperate zone-1 (<2400 m) and warm temper-ate zone-2 (2400-2600 m). The rest of the zones were taken as they are i.e. cool temperate zone (2600-3600 m) and alpine zone (> 3600 m). These adjustments in the limits of agro-ecological zones were done for analysing the spatial variations in physiography, climate factors, cropping pattern and their impact on the rice production and its yield.

The elevation data was also used to analyse the impact of slopes on the rice production in the study area. Any standard classification of cultivable slopes in Bhutan was not available because some of the wetland cultivation is also carried out by carving terraces in the areas having more than 27 degrees slope, which generally is considered unsuitable for irrigated cultivation. Howev-er, based on the field observations and previous experiences, the slopes of the area covered under the wetlands were classified into five categories i.e. 0-7 degrees (Gentle), 7-14 degrees (Moder-ate), 14-18 degrees (Moderately Steep), 18-27 degrees and more than 27 degrees (Very Steep).

All the data processing, spatial analysis and map preparation was carried out with the help of

ESRI software ArcGIS version 10.2. The visualisation of the location of the wetlands in virtual 3D environment was done by overlaying the vector layer on the google earth. Results and Discussion 1. Physiography and Wetland

The results show that about 45 percent of the total area of Paro Dzongkhag falls in the Alpine agro-ecological zone (Table 1 and Map 2) and this is not suitable for crop cultivation. The sec-ond highest proportion of the total area falls in the cool temperate zone but the percentage of the wetland area in this zone is less than 1 percent which is located at the lower limits of the zone. The warm temperate zones 1 and 2 constitute only 13.34 percent of the Dzongkhag area but al-most all the wetlands are found in these zones. However, the largest proportion of the wetlands, i.e. 82.56 percent, is located in the warm temperate zone-1 and only about 16.59 percent in the warm temperate zone-2 (Map 3). The huge difference in the area of wetlands across the agro-ecological zones clearly suggests that the quality of the conditions favourable for rice cultivation deteriorate as the elevation increases and the two conditions strongly related to altitude are slope and climate so the analysis of these two aspects has been discussed in the following sections.

Agro-Ecological Zone Area of Paro Dzongkhag Area of Wetland Hectare Percent Hectare Percent

> 3600 m - Alpine 57365 44,57 0 0,00 2600-3600 m - Cool Temperate 54161 42,08 15 0,85 2400-2600 m - Warm Temperate-2 9256 7,19 292 16,59 < 2400 m - Warm Temperate-1 7918 6,15 1453 82,56 Total 128700 100,00 1760 100,00

Table 1. Location of Wetlands in Different Agro-Ecological Zones




Map 2. Agro-ecological Zones of Paro Dzongkhag The distribution of the wetland in relation to slope shows that about 48 percent of it is located

in the gentle slope zone and further 35 percent in the areas having moderate slope (Table 2 and Map 3). Most of the wetland in these slope zones is located along the banks of the main rivers and partially along some tributaries because the soils in these stretches are very fertile. The gen-tle and moderate slopes have minimal risk of soil erosion so not such prevention measures are required. The proportion of the wetland in the zones having moderately steep, steep and very steep slopes about is 8, 7 and 1 percent respectively. The soils in these slope zones are mostly coarse, stony and unproductive so these are not suitable for crop cultivation on regular basis. The local practices show that largely these zones are used for growing fodder grasses and animal grazing but also some crops are sown in small pockets occasionally.

Slope Category Area of Paro Dzongkhag Area of Wetland

Hectare Percent Hectare Percent > 27 Degrees - Very Steep 60500 47,01 20 1,15 18 27 Degrees - Steep 35400 27,51 130 7,47 14 – 18 Degrees -Moderately Steep 12200 9,48 140 8,05 7 – 14 Degrees - Moderate 15200 11,81 610 35,06 < 7 Degrees - Gentle 5400 4,20 840 48,28 Total 128700 100,00 1740 100,00

Table 2. Area under different Slopes Categories




Map 3. Location of Wetland in Different Agro-Ecological Zones and Slope Categories

2. Rainfall Requirements of Rice Crop The rice cropping season in Paro Dzonghag is from June to September and, normally, it

stretches over 119 to 121 days (Shah et al., 2011; Zawawi et al. 2010). There are two main stages of this crop i.e. pre-saturation stage of about 14 days and, growth and maturation stage of about 105 days. The water requirements of rice plants are different in each of the two stages (Table 3). The relationship between precipitation and temperature data recorded at Drugyel Dzong and Paro DSC meteorological stations during rice cropping season and the yield of rice in the Ge-wogs surrounding each of these stations has been analysed. Both types of the datasets pertain to 6 year between 2004 and 2011 as the required data for 2008 and 2010 are missing.

Drugyel Dzong station is located in the Warm Temperate Zone-2 (Map 3) and the two Ge-

wogs closer to this station are Tsento and Doteng.




Paro DSC station is located in the Warm Temperate Zone-1 (Map 3) and the seven Gewogs covered by this are Lamgong, Dobshari, Wangchang, Hoongrel, Loongnyi, Shapa and Doga.

The tenth Gewog, Nagya, doesn’t have any rice cultivating area so this has not been included in the analysis.

Stage of Rice Crop Water Requirement References

Overall Rice cultivation period (119 days) 775 mm Zawawi, Mustapha and Passau (2010)

Pre-saturation period (14 days) 329 mm Shah et al. (2011) Growth period (105 days) 446 mm Shah et al. (2011)

Table 3. Water Requirements of Rice Crop during different Stages of Cultivation

3. Climatic Factors and Rice Yield in Warm Temperate Zone-2 The results shows a high positive correlation (r = 0.58) between the amount of rainfall and the

yield of rice in the warm temperate zone-2 (Figure 1). The total rainfall in this zone ranges from 398 mm in 2005 to 1184 mm in 2009 and the rice yield ranges from 133700 kg/ha in 2001 to 186400 kg/ha in 2009. The overall water requirement during a rice growing season is estimated to be 775 mm (Table 3) which was not fulfilled except in 2009 and, as a result, the highest rice yield was also recorded in this year. Most of the wetland in this zone has moderate slope (Map 2) and it is not feasible to supplement the water shortage in the fields through irrigation from river water which clearly has an impact on the rice yield during the years having lower rainfall.

Figure 1. Rainfall at Drugyel Station and Rice Yield in Tsento and Doteng Gewogs

Figure 2. Temperatures at Drugyel Station and Rice Yield in Tsento and Doteng Gewogs

The average temperature of the four rice copping months and the yield of rice in the warm temperate zone-2 also shows a positively correlation, i.e. r = 0.65 (Figure 2). The lower availa-

A B

r = 0.60

A B

r = 0.67




bility of water from rains during the cropping season and limited source of irrigation, even slight variation in the temperatures causes considerable adverse impact on the yield of rice.

4. Climatic Factors and Rice Yield in Warm Temperate Zone-1

There is an insignificant inverse correlation (r = -0.03) between the amount of total rainfall received during the rice cropping season and yield of rice in the warm temperate zone-1 (Figure 3). The total rainfall ranges from 261 mm in 2009 to 452 mm in 2011 and this amount is far be-low the overall water requirement of 775 mm during the rice cropping season (Table 3). Since most of the wetland in this zone have gentle slope and is located along the main river and some tributaries which makes it easier to construct irrigation channels for and supplementing the water shortage. It is observed that heavy rainfall, e.g. the highest rainfall of 1162 mm was received in 2006 but the rice yield (4500 kg/ha) in this year was 150 kg/hectare less than in 2005 (4649 kg/hectare). In fact, heavy rainfall in this year was received during the months of August and September which caused some damage to the rice during the maturation and harvesting phases. It is not only the total amount of rainfall received during the rice cropping season that is important but also its intensity, distribution and timing of rain within this period affects the yield of rice.

Figure 3. Rainfall at Paro DSC Station and Rice Yield in the 7 Surrounding Gewogs

Since the wetland in this zone has sufficient irrigation facilities so the temperatures between 15oC and 34oC are considered suitable for fetching good yield of rice (Morita et al., 2004 and Ghimaray, 2012). The average temperatures of rice cropping season in various years ranges from 19oC to 23oC, and this falls well within the range suitable temperatures. However, temperatures and rice yield show a negatively correlation (r = -0.54) in the areas below 2400 m.

Figure 4. Temperature at Paro DSC Station and Rice Yield in the 7 Surrounding Gewogs

Conclusions A very large proportion of the wetland in Paro Dzongkhag, about 83 percent, is located in the

warm temperate zone-1 (below 2400 m) and the remaining 16.59 percent in the warm temperate zone-2 (2400-2600 m). Most of the wetland in the warm temperate zone-1 is situated along the

A B

r = -0.03

A B

r = -0.54




main river and some tributaries, and has gentle slopes so these areas have good irrigation facili-ties. On the other side, most of the wetland in the warm temperate zone-2 is located along the narrow valleys of the river tributaries and has moderate slopes which make the irrigation difficult and increases dependence on weather conditions. Resultantly, there is a positive correlation of the yield of rice with the amount of rainfall, i.e. r=0.60, received during the rice cropping season as well as with the average monthly temperatures during this season i.e. r=0.60. However, this correlation is negative in the warm temperate zone-1 i.e. r= -0.03 with rainfall and r= -0.57. Though the aerial distance between the location of the two meteorological stations in the study area is less than 20 kms, the variations in physiographic and associated climatic factors cause much difference in the yield of rice between these two agro-climatic regions. In the absence of high temporal climate data, it is difficult to assess the impact of climate change on agriculture, but weather abnormalities have been affecting the yield of rice in Bhutan. Acknowledgements

The authors are thankful to Dr. Shahnawaz (University of Salzburg, Austria) for his construc-tive suggestions which improved the quality of this paper tremendously. Thanks are also due to the College of Natural Resources, Lobesa, Royal University of Bhutan for publishing the paper. References IPCC (2007). Climate Change 2007-Syntesis Report. Inter-governmental Panel on Climate Change

<www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_synthesis_report.htm>. Accessed 15 August 2015.

Karn, P.K (2014). The Impact of Climate Change on Rice Production in Nepal, (SANDEE Working Pa-pers, ISSN 1893-1891; WP 85–14). <www.sandeeonline.org/uploads/documents/publication/1032_PUB_Working_Paper_85_Prakash.pdf>. Accessed 15 August 2015.

Minten, B. & Chencho, D. (2010). Technology adoption and productivity in Bhutan; Agricultural and food policy research and capacity strengthening project. <www.ifpri.org/sites/default/files/publications/bhutannote03.pdf>. Accessed 3 November 2013.

MoAF (2010). Agriculture Statistics. <www.moaf.gov.bt/moaf/?wpfb_dl=494> Accessed 15 August 2015.

MoAF (2011). Bhutan Land Cover Assessment 2010, National Soil Services Centre (NSSC) & PPD, MoAF, Royal Government of Bhutan, Thimphu, Bhutan.

Morita, satoshi; Yonemaru, Jun-Ichi and Takanashi, Jun-Ichi (2005). Grain Growth and Endo-sperm Cell Size Under High Night Temperatures in Rice (Oryza sativa L.). Annals of Botany, 95, pp. 695–701.

NSB (2014). Statistical Yearbook of Bhutan 2014. National Statistics Bureau, Royal Govern-ment of Bhutan, Thimphu, Bhutan.

Shah, F., Huang, J., Cui, K., Nie, L., Shah, T., Chen, C., Wang, K. (2011). Impact of high-temperature stress on rice plant and its traits related to tolerance. <http.//dx.doi.org/10.1017/S0021859611000360>. Accessed 15 August 2015.

Shahid, S. (2011). Impact of climate change on irrigation water demand of dry season Boro rice in north-west Bangladesh. Climatic Change, 105(3-4), 433-453. doi. 10.2307/210739. <http.//dx.doi.org/10.1007/s10584-010-9895-5>. Accessed 15 August 2015.

Tobgay, S. (2005). Agriculture diversification in Bhutan. <www.moaf.gov.bt/moa/downloads/downloadFiles/MoADownload4ig6471vj.pdf>. Accessed 15 Au-gust 2015.

Toriman, M. E., et al. (2013). Paddy Production and Climate Change Variation in Selangor, Malaysia. Asian Social Science, 9(14), 55-62.

Zawawi , M.A.M; Mustapha, Sa’ari, Puasa, Zuzana (2010. Determination of Water Requirement in a Paddy field at Seberang Perak Rice Cultivation Area. Journal - The Institution of Engineers, Malaysia, Vol. 71, No.4, pp. 32-41.

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The Impact of Physiography and Weather Abnormalities on ... · PDF file2 Sherubtse College, Royal University of Bhutan, Kanglung, Bhutan Abstract Rice is the staple food for a majority