Assessing the Impact and Adaptation of Climate Change on Effective Rainfall for Agricultural Water Management

氣候變遷下有效雨量對農業用水管理之衝擊及調適策略評估

FENG-WEN CHEN(陳豐文) ； CHEN-WUING LIU(劉振宇)

《台灣水利》 70卷2期 (2022/06) Pp. 1-29

https://doi.org/10.6937/TWC.202206_70(2).0001

摘要

Taiwan is a country of abundant annual rainfall but is also a country at high risk of water deficiency. Rainfall has been seen as the primary source of irrigation for crop growth from the past to now; hence, effective rainfall (ER) has become a critical factor in crop irrigation in Taiwan. Through climate change, rainfall patterns and stream runoff have altered drastically causing increased frequencies in some phenomena such as drought and other water-related disasters, as well as difficulties in water resource allocation. This has put an increased pressure on irrigation to satisfy the water resource that crops require. Hence a precise evaluation and high application of ER was considered one of the most suitable solutions for the future. The Taichung Irrigation Area (TIA) mainly takes water from rivers and potentially suffers from water shortage was selected as the research objective in this study. The ER estimation model was established to estimate ER in paddy fields and upland fields. In this study, rainfall data from 12 TIA rainfall stations from 1961 to 1990 were used to analyze ER variations under the impact of climate change. To conduct the impact assessment of ER under the influence of climate change, ten types of GCMs Three optimal GCMs such as GFCM20, HADCM3, and MRCGCM are selected in this research. The simulation was adopted in three scenarios of A2, A1B, B1 for the short-term, mid-term, and long-term predictions using TaiWAP model. The results show that the ER increases in flood seasons but decreases in dry seasons. In addition, variations in mountain areas are more significant than those in seashore areas. To reduce the impact of climate change, the following three adaptation strategies are proposed: (1). adjustment of the cultivation period, (2). adjustment of ridge height, (3). conversion from paddy field to upland field. The exposure and the water shortage index are adopted to evaluate the performances of vulnerability for these three strategies. Adjusting ridges to 300 mm height is the optimal strategy and is recommended. The second priority is the conversion from paddy field to upland field. Adjustment of the cultivation period is not recommended due to the worse performance of vulnerability.

關鍵字

Effective rainfall (ER) ； Agricultural water management ； Climate change ； Vulnerability ； Adaptation strategy

並列摘要

臺灣為高雨量及高度缺水風險的國家，降雨是作物生長主要用水來源；有效雨量的估算為關鍵因子。受氣候變遷強化的效應，河川逕流及降雨現象均受改變，水庫配水面臨調配困難現象。以河川為主要用水來源的灌溉區域亦面臨高頻率的缺水現象。因此有效雨量的評估及高效率應用於灌溉為解決河川缺水風險下的方法之一。本文以潛在缺水的河川取水型灌區－臺中灌區為研究區域。有效雨量的計算包含稻作及旱作的有效雨量。雨量資料則採用12處雨量站於1961-1990年（共30年）的日雨量進行評估。氣候變遷對於有效雨量的衝擊影響評估，本文採用GFCM20、HADCM3、MRCGCM等3種基期資料與研究區域之雨量及溫度均具高相關性（相關係數＞0.8）的GCM模式，進行A2、A1B、B1等3種情境下之短期、中期及長期的衝擊模擬；結果顯示有效雨量均於3種情境下呈現豐水期增加而枯水期減少的共同趨勢，趨勢由高海拔山區往低海拔的沿海灌區更為顯著。因應氣候變遷對有效雨量的衝擊影響，本文提出3項調適措施進行提高有效雨量利用之策略，分別為（1）.調整耕種時期、（2）.調整田埂高度、（3）.作物轉作等；本文重新計算有效雨量並以曝露度及缺水指標之乘積進行脆弱度分析，以作為有效雨量應用於農業灌溉用水因應氣候變遷影向下之調整策略擬定；結果顯示以調整田埂高度至300 mm的措施為最佳、水稻轉作為和作物栽培次之、調整耕種時期的策略效果則不顯著。

並列關鍵字

有效雨量 ； 農業用水管理 ； 氣候變遷 ； 脆弱度 ； 調適策略

參考文獻

Bosen JF (1960) A formula for approximation of saturation vapor pressure over water. Monthly Weather Reviews. 88(8): 275-276.

Chen CG, Xie DX, Zhen L (2007) Characters of precipitation variation in Jinghe watershed. Resource Science. 29(2): 172-177.

Chen FW, Liu CW (2012) Estimation of the spatial rainfall distribution using inverse distance weighting (IDW) in the middle of Taiwan. Paddy and Water Environment. 10(3): 209-222.

Chen S, Lee TT (1964) Estimation of water requirements for rice irrigation by moisture equivalent.Journal of Chinese Agricultural Engineering. 10(4):15-40.(In Chinese)

Doorenbos J, Pruitt, WO (1973) Guidelines for Predicting Crop Water Requirements. FAO Irrigation and Drainage Paper 24, Rome, Italy.