利用品質適栽度模型探討氣候變遷對水稻外觀品質之衝擊與調適策略

Abstract

台灣近三十年水稻之生產目標已從產量轉向品質。然而，近年溫室效應導致全球暖化與降雨時空間分布不均等現象已對水稻生產環境造成負面影響，並使兩期作插秧時序分別提前與延後。未來在氣候變遷影響下，預期台灣兩期作水稻栽培環境將更加嚴峻，衝擊產量及品質。本研究透過影響品質的主要環境因子─溫度對影響品質的主要性狀─白堊質粒率的影響，建立品質適栽度模型，在適栽度分析之架構下結合地理資訊系統預測未來台灣水稻品質適栽區域之時空間變化趨勢。本研究先以2001至2014年之氣溫資料透過模型估算期間內各期作之品質適栽度，與歷年白堊質粒率進行相關性分析，證實品質適栽度與白堊質粒率間有顯著的相關性 (r = -0.311***)，顯示本模型估算之品質適栽度能有效反映溫度對品質造成的影響。本研究將台灣地區IPCC AR5 統計降尺度RCP 4.5及RCP 8.5兩種情境之未來氣候預測資料，利用驗證後的模型估算兩期作品質適栽度並探討其空間差異。結果顯示未來在RCP 4.5或RCP 8.5情境下，至世紀末 (2081-2100年) 時水稻兩期作將因充實期溫度上升，導致品質大幅下降，尤其中南部水稻主要產區特別嚴重。根據上述結果，本研究從時間與空間的角度，探討未來水稻栽培期與適栽區域之可行的調適策略。在時間調適策略方面，透過評估不同時間抽穗對品質之影響，結果顯示RCP 4.5情境下至世紀末全台兩期作最適抽穗時間將分別提前及延後2旬；RCP 8.5情境下則為3旬。若在追求最佳品質和維持現有品質此兩種目標下推估插秧期，並考慮冬季低溫及低日照之環境對水稻生育之威脅後，未來一期作可以維持現有品質為目標設定栽培期，其插秧期建議提前至12月上旬至2月中旬；而二期作則以最佳品質為目標設定栽培期，其插秧期建議延後至7月下旬至10月上旬。在空間調適策略方面，從本研究結合品質適栽度、分蘗期適栽度及供水適宜度綜合評估水稻合適產區之適栽度分析結果顯示，目前水稻主要產區至世紀末可能無法維持穩產優質的水稻生產。若考慮至2035年之前可行的水稻合適產區規劃，則目前水稻主要產區未來可能不需要進行調整，可透過栽培管理上的調適方法因應氣候變遷造成之衝擊。若考慮至世紀末時仍能有穩產優質潛力之合適產區，則建議以花東地區之玉里至鹿野一帶，中部地區之大甲至豐原、霧峰至竹山一帶作為台灣未來具穩產優質潛力之水稻合適產區。若要維持現有的水稻產量水準，從農業統計年報資料推估兩期作合計需258.2千公頃的收穫面積，本研究所規畫之合適產區若是在RCP8.5情境下，則預估兩期作合計僅剩111.2千公頃，顯示未來水稻生產恐無法同時兼顧產量及品質。

In the past thirty years, the purpose of rice production in Taiwan has changed from yield to quality. However, the global warming and the uneven distribution of rainfall caused by the greenhouse effect have already had a negative impact on the environment for rice production, even have caused the shift of cultivation timing. It's expected that both 1st and 2nd crop in Taiwan will be more negative impacts on rice yield and quality under the climate change. In this study, we built a suitability model of quality considered by the relationship between temperature and chalky grain ratio, and then we used this model to evaluate a GIS-based suitability analysis for rice quality in the future of Taiwan. We assessed the quality suitability through the model using the temperature data during 2001-2014, and the correlation analysis indicated that the quality suitability was significantly associated with chalky grain ratio. (r = -0.311***) It means that it's effective to assess the effect between temperature and rice quality by this model. The impacts of RCP 4.5 and 8.5 scenarios in the IPCC AR5 on rice quality suitability were assessed by using statistically downscaled climate projections as inputs into the suitability model of quality. The results showed that the quality of rice will decrease significantly due to the temperature rising during grain-filling stage at the end of the century (2081-2100) under RCP 4.5 and 8.5 scenarios, especially in the major rice production zones in central and southern Taiwan. According to the results, we explores the feasible strategies from the perspective of timing and space for the future for rice cultivation timing and suitable area. For timing adaptation strategy, we explored the feasible cultivation timing by assessing the impact of different heading dates on rice quality. The results indicated that under the RCP 4.5 scenario, the optimal heading timing for best quality will move forward or backward 2 ten-days in the 1st crop or the 2nd crop at the end of the century, and it will move forward or backward 3 ten-days in the case of the RCP 8.5. We evaluated the transplanting timing under the two objectives of 'pursuing the best quality' and 'maintaining the existing quality', considering the threat to rice growth in low temperature and low solar irradiance in winter. The results suggest that the transplanting timing should be advanced to early December to mid-February to maintain the existing quality for rice production in the 1st crop. In the 2nd crop, the transplanting timing should be delayed until late July to early October to pursue the best quality. For spatial adaptation strategy, we developed a suitability map for rice crop based on rice quality suitability, tillering suitability and water supply suitability. The results showed that the major rice production zones will be almost excluded from the suitable zones at the end of the century. To planning the suitable zones for rice production by 2035, the current major rice production zones may not need to be adjusted, and the impact of climate change can be overcome by the adaptation strategies of cultivation management. To planning the suitable zones for rice production by 2100, the results are suggested that the parts of eastern and central Taiwan (especially from Yuli to Luye, Dajia to Fengyuan, and Wufeng to Zhushan) can be planned as rice production zones for both high quality and stable yield.