摘要：陸地上的水文過程在全球及局部氣候扮演了重要的角色。就像海洋提供下邊界條件給大氣，陸地的水文過程提供了由土壤、湖泊的蒸發以及植物的蒸散給大氣。而不同的植披、土壤成份與地形等因素，更加深了陸地水文過程的複雜性，同時也深刻地影響著陸地與大氣的交互作用。因此，了解陸地水文過程對氣候的影響將有助於改善氣候模式進而提升氣候模擬的準確度。相較於表層土壤水分與大氣之間的快速交互作用，地下水對氣候的影響是屬於較長時間尺度的，也因此地下水扮演相當重要的緩衝角色。當有降水時，因為土壤可以儲存的水有限，所以大部分的水除了從地表蒸發回大氣或是經由河川流到海洋，其餘的都會流到底下成為地下水。而當乾旱或乾季時，地下水即可透過蒸散作用成為大氣中水氣的來源，並可緩衝河流流量的季節變化。
我國科技部與法國科技署所簽署之雙邊協議合作計畫提供了一個相當獨特的機會與法國研究團隊進行合作。此計畫的主要目標是藉由模式的發展、模擬與分析來探討地下水對區域和全球氣候以及水資源的影響。此次與法國的合作，我們將利用三種不同的氣候模式來探討地下水對氣候的影響。其中法國團隊所使用IPSL和CNRM-GAME兩個單位的氣候模式已納入IPCC（聯合國政府間氣候變遷專門委員會）報告中，而台灣團隊則改進與使用美國國家大氣研究中心的氣候模式（Community Earth System Model）。雙方均曾參與國際上對於模式結果互相比較的計畫（model intercomparisons），也對於模式皆有相當程度的理解。IPSL與台灣團隊已率先在氣候模式對於地下水做敏感度的分析，而CNRM-GAME則發展了更優越的全球地下水參數化過程。基於這些條件，並將此合作計畫分為以下四個任務（此計畫並將舉辦兩次國際研討會）：
T1: 固定地下水位深度（fixed WTD）在三種氣候模式中的敏感度測試。
T2: 在模式中加入合理的地下水與土壤水分相互作用的參數化過程（active WTD），以了解地下水變化對氣候的影響，以及陸地與大氣的交互作用。
T3: 了解動態地下水位深度（active WTD）和氣候變遷之間的相互影響。在這裡有兩個相輔相成的問題（1）什麼是地下水對氣候變化的影響？（2）什麼是氣候變化對水資源（含地下水）的影響？
T4: 了解動態地下水位深度（active WTD）與人為抽取地下水之交互作用，以及對氣候的潛在影響。
此計畫（I-GEM）將加強法國和台灣在地球科學上跨領域的研究潛力，與全體研究團隊在國際上的研究知名度，我們將舉辦兩次國際研討會（一次在台灣，一次在法國），藉以與歐洲、亞洲與北美的科學家合作，對地下水在氣候模式中扮演的角色有更深入的了解。
Abstract: Groundwater (GW) constitutes 30% of the fresh water resources, which are subjected to increasing withdrawals. When shallow enough, it can also sustain soil moisture, thus increase evapotranspiration, with potential impact on the climate system (in particular temperatures and precipitation). Its large residence time can also increase the Earth system’s memory, with consequences on the persistence of extreme events, hydro-climatic predictability, and anthropogenic climate change, particularly the magnitude of regional warming. Our main goal is to explore the impacts of GW on regional and global climate, and its links to water resources availability, through model analyses. To this end, our Franco-Taiwanese consortium offers a unique opportunity to compare the sensitivity of simulated climate to different GW parameterizations within 3 different climate models: the French IPSL and CNRM-GAME climate models, and the American NCAR climate model (CESM), modified and used here by the Taiwanese team.
All teams have experience in international intercomparison projects, and they have all recently emerged as important actors of the research on GW in climate models: the IPSL team and Taiwanese team have pioneered the analysis of the sensitivity of global simulated climate to GW, while the CNRM-GAME team achieved significant advances regarding the global-scale parameterization of GW and its coupling with rivers and land surfaces.
The project includes two transversal tasks: T0. Coordination; T5. International workshops; and the research program is organized into 4 successive scientific tasks:
T1. Sensitivity to fixed water table depths (WTD), to identify the patterns of “active WTD”, below which GW do not impact regional climate.
T2. Dynamic WTD over the recent period, to assess the potential of realistic GW parameterizations to improve the simulated climate, with a focus on land/atmosphere feedback and the persistence/memory in the Earth system
T3. Dynamic WTD and climate change, with two complementary questions: (1) What is the influence of GW on the climate change trajectory? (2) What is the impact of climate change on water resources (including GW)?
T4. Dynamic WTD with withdrawals, which artificially increase soil moisture via human activities, with potential impacts on climate until water resources get exhausted.
I-GEM is also intended to consolidate the potential of France and Taiwan in the interdisciplinary research field of the global water cycle, by tightening the links between these two countries, and by federating the French community (IPSL and CNRM-GAME) and Taiwanese earth science community. We also aim at enhancing the visibility of French and Taiwanese teams, by developing closer links with European, Asian, and North-American leaders in large-scale modeling of GW. To this end, we want to organize two international workshops on the role of GW in climate models, one in Taiwan and one in France, with a broad audience (T5).
