臺灣位於板塊交界帶，地表起伏極為劇烈，在極短距離海拔高度急速拔升，因此造成臺灣河流長度較短及坡度較大等特性。河川流量在探討水資源管理、洪水及乾旱等研究皆占據重要的角色，近年來全球受到氣候變遷影響使得降雨型態發生改變，造成降雨時空分佈不均且逐漸出現降雨兩極化的現象。台灣位於亞熱帶氣候區，屬乾濕季分明之地區，因此降雨兩極化的現象更加的明顯，而河川流量受到降雨量影響甚巨，使得河川流量於豐水期及枯水期流量的差異更加的擴大，造成乾旱事件發生。為了有效管理日益短缺之水資源，須針對河川流量之趨勢及乾旱特性進行探討及評估。國內過去探討乾旱的研究多以降雨量資料進行評估，極少以河川流量之角度進行評估及分析，而台灣河川為水資源主要來源，更是進行區域性水資源分配及規畫的重要角色，因此本研究所進行之河川流量趨勢及河川乾旱特性分析結果可提供給相關水資源應用評估及規畫之重要參考資訊。
本研究首先以臺灣北部地區8個河川流量站長時間之流量資料利用Mann-Kendall 檢定法進行年平均流量、逐月月平均流量和高低流量的趨勢分析。另外以Theil-Sen 斜率推估法進行趨勢斜率的計算，接著以Mann-Whitney-Pettit檢定法和Cumulative Deviation 檢定法進行改變點分析，探討改變點並瞭解改變點前後之變化差異性。再以臺灣北部區域8個河川流量站與鄰近8個雨量站資料為基礎，以河川乾旱指標(SDI)法及標準化降雨指標(SPI)法進行水文及氣象型乾旱的時空特性分析。另以Mann-Kendall檢定法分析河川乾旱指標(SDI)及標準化降雨指標(SPI)，探討水文及氣象型乾旱長時間趨勢特性。最後以馬可夫鍊評估蘭陽溪流域乾旱發生機率。
河川流量趨勢結果顯示，以Mann-Kendall 檢定法進行年平均流量分析研究區域8 個流量站 中，僅有蘭陽溪流域的西門橋站具有顯著下降之趨勢。上升趨勢大多數分布於淡水河、鳳山溪及頭前溪流域，蘭陽溪流域則多數為下降趨勢。本研究區域僅有西門橋流量站具有改變點出現，西門橋站改變點前後年平均流量量達44.09%，年平均流量於改變點後呈現下降。各流量站逐月月平均流量之趨勢檢定結果顯示，春季上升趨勢主要集中於淡水河及頭前溪流域，下降趨勢則位於蘭陽溪與鳳山溪流域；秋季上升趨勢主要在頭前溪流域，下降趨勢則集中在蘭陽溪、淡水河及鳳山溪3流域中。雨量趨勢結果顯示，以Mann-Kendall 檢定法進行年平均流量分析研究區域8 個雨量站中，頭前溪流域的梅花及太閣南站具有顯著上升之趨勢。本研究區域僅有太閣南雨量站具有改變點出現，太閣南站改變點後年雨量上升15.8%。各雨量站逐月雨量之趨勢檢定結果顯示，春季下降趨勢主要集中於蘭陽溪及鳳山溪流域，上升趨勢則位於頭前溪流域；夏季上升趨勢主要在鳳山溪和頭前溪流域。
乾旱特性分析結果顯示，臺灣北部區域於2002至2003年呈現較嚴重之乾旱，該年度同時出現水文型及氣象型乾旱，且水文型乾旱之強度較氣象型乾旱嚴重。由過去歷史紀錄可知，2003年為歷史上臺灣地區乾旱較嚴重之年度，該年度之河川流量為近40年中最低。SDI及SPI趨勢分析結果顯示，北部區域除了蘭陽溪流域，其餘流域在水文及氣象型乾旱的趨勢上皆不顯著，而蘭陽溪流域在氣象及水文型乾旱趨勢上皆具有顯著下降的趨勢，且蘭陽溪流域之乾旱強度在未來有增加的現象。另外，由馬可夫鏈法分析乾旱事件之發生機率結果可觀察出，蘭陽溪流域發生乾旱事件之機率較宜蘭河流域高，尤其極端事件發生之機率，蘭陽溪流域於枯水期(11至4月)發生極端乾旱的機率為20.6%，宜蘭河流域則為3.4%。本研究結果顯示，分析乾旱及潮濕事件發生機率時，可由馬可夫鏈法以短時間之乾旱事件強度的發生頻率及機率的結果，預測長時間乾旱及潮濕事件強度之發生機率。

Taiwan is located at the boundary between the Philippine Sea Plate and the Eurasian Plate and featured violent plate activity and rapidly rise in terrain altitude. The plate activities had resulted in shorter river lengths and steeper terrains. Concerning streamflow, it is an important factor in the study of water resource management, floods, and droughts. The impact of global climate change in recent years has led to changes in rainfall patterns, resulting in uneven rainfall distribution and the birth of polarized rainfalls. Taiwan is a region located in a subtropical climate zone and one that is characterized by distinct wet and dry seasons; such a characteristic has created a comparatively more severe polarized rainfall situation in which streamflow is drastically influenced by amount of rainfall. This has created considerable differences in streamflow between wet and dry seasons and instances of hydrological droughts are prevalent. Therefore, to effectively manage the increasingly scarce water resources, streamflow characteristics during dry seasons must be explored and assessed.
In this study, the long-term streamflow and precipitation data and trends recorded at the gauging station in the Northern Taiwan regions were analyzed using the Mann-Kendall test. The data used for trend analysis comprised the average annual streamflow, the average seasonal streamflow, and the high and low flows. Subsequently, the slope trend was calculated using the Theil-sen estimator. Finally, the change point analysis was conducted using the Mann-Whitney-Pettit test and the Cumulative Deviation test to gain further information about the change points and to understand the changes in streamflow before and after the change points. And to analyze the spatial and temporal characteristics of hydrological and meteorological droughts, this study employed Streamflow Drought Index (SDI) and Standardized Precipitation Index (SPI) based on data from 8 streamflow gauging stations and 8 nearby precipitation stations in northern Taiwan. The Mann-Kendall trend tests were performed to investigate the long-term trends of hydrological and meteorological droughts. Finally, the Markov chain is used to analyze the occurrence probability of hydrological of Lanyang River basin.
The streamflow results showed that of the eight gauging stations, only the Ximen Bridge Station in the Lanyang River basin show a significant downward streamflow trend. Results of the monthly and seasonal average streamflow analysis show that in the spring, 72.2% of the gauging stations showed upward streamflow trends, most of which were located in the Tamsui River and the Touqian River basins. The high and low flow data analysis shows that the Ximen Bridge Station was the only gauging station to feature a significant downward streamflow trend for both high and low flows. The precipitation results showed that of the eight stations, the Meihua amd Taigena Station in the Touqian River basin show a significant downward precipitation trend. Results of the monthly and seasonal precipitation analysis show that in the spring, 54.2% of the stations showed upward precipitation trends, most of which were located in the Lanyang River and the Fengshan River basins. On the other hand, the results of drought properties demonstrated that more severe droughts took place in northern Taiwan between 2002 and 2003. During this period, hydrological and meteorological droughts occurred simultaneously while the former was more intense. Historical records indicated that relatively serious droughts took place in 2003 in Taiwan and streamflow reached its minimum over the recent 40 years.
Trend tests on SDI and SPI revealed that there are no significant trends for both hydrological and meteorological droughts in northern Taiwan, except for the Lanyang River catchment area. Decreasing trends for both types of droughts were found in the Lanyang River catchment, but droughts of increasing intensities in the future were noted. In addition, analysis of drought occurrence probabilities using the method of Markov chains has shown that the occurrence probabilities of drought events are higher in the Lanyang River basin than in the Yilan River basin; particularly for extreme events, the occurrence probability of an extreme drought event is 20.6% during the dry season (November to April) in the Lanyang River basin, and 3.4% in the Yilan River basin.

1.Al-Faraj, F.A.M., Scholz, M. and Tigkas, D., Sensitivity of surface runoff to drought and climate change: Application for shared river basins. Water, 2014, 6, 3033–3048.
2.Baggaley, N.J., Langan, S.J., Futter, M.N., Potts, J.M. and Dunn, S.M., Long-term trends in hydro-climatology of a major Scottish mountain river. Sci. Total Environ., 2009, 407, 4633–4641.
3.Balocchi, F., Pizarro, R., Meixner, T. and Urbina, F., Annual and monthly runoff analysis in the Elqui River, Chile, a semi-arid snow-glacier fed basin. Tecnologia y Ciencias del Agua, 2017, 8(6), 23-35.
4.Bassiouni, M. and Oki, D.S., Trends and shifts in streamflow in Hawai’i, 1913–2008. Hydrol. Process., 2013, 27, 1484–1500.
5.Boudad, B., Sahbi, H. and Manssouri, I., Analysis of meteorological and hydrological drought based in SPI and SDI index in the Inaouen Basin (Northern Morocco). Journal of Materials and Environmental Sciences, 2018, 9(1), 219-227.
6.Buishand, T.A., Some methods for testing the homogeneity of rainfall records. Hydrol. Process., 1982, 314, 312–329.
7.Chattopadhyay, S., Edwards, D.R., Yu, Y. and Hamidisepehr, A., An Assessment of Climate Change Impacts on Future Water Availability and Droughts in the Kentucky River Basin. Environmental Processes, 2017, 4(3), 477-507.
8.Chen, L., Singh, V.P., Guo, S.L., Mishra, A.K. and Guo, J. Drought analysis using Copulas. J. Hydrol. Eng., 2013, 18, 797–808.
9.Chen, Z., Chen, Y. and Li, B., Quantifying the effects of climate variability and human activities on runoff for Kaidu River Basin in arid region of northwest China. Theor. Appl. Climatol., 2013, 111, 537–545.
10.Chung, Y.D., Kuo, C.C. and Chen, C.S., The temporal variation of regional rainfall characteristics in Taiwan. J. Chin. Agric. Eng., 2009, 55, 1–18.
11.Dams, J., Salvadore, E., van Daele, T., Ntegeka, V., Willems, P. and Batelaan, O., Spatio-temporal impact of climate change on the groundwater system. Hydrol. Earth Syst. Sci., 2012, 16, 1517–1531.
12.De Martino, G., Fontana, N., Marini, G. and Singh, V.P., Variability and trend in seasonal precipitation in the continental United States. J. Hydrol. Eng., 2013, 18, 630–640.
13.Diop, L., Yaseen, Z.M., Bodian, A., Djaman, K. and Brown, L., Trend analysis of streamflow with different time scales: a case study of the upper Senegal River. ISH Journal of Hydraulic Engineering, 2018, 24(1), 105-114.
14.Dixon, H., Lawler, D.M. and Shamseldin, A.Y., Streamflow trends in western Britain. Geophys. Res. Lett., 2006, 33, L19406.
15.Do, H.X., Westra, S. and Leonard, M., A global-scale investigation of trends in annual maximum streamflow. Journal of Hydrology, 2017, 552, 28-43.
16.Dudley, R.W., Hodgkins, G.A., McHale, M.R., Kolian, M.J. and Renard, B., Trends in snowmelt-related streamflow timing in the conterminous United States. Journal of Hydrology, 2017, 547, 208-221.
17.Duhan, D. and Pandey, A., Statistical analysis of long term spatial and temporal trends of precipitation during 1901–2002 at Madhya Pradesh, India. Atmos. Res., 2013, 122, 136–149.
18.Esty, D., Srebotnjak, T., Goodall, M., Andonov, B., Campbell, K., Gregg, K., Kim, C., Li, Q., Martinez, M. and Townsend, J., et al. Environmental Sustainability Index: Benchmarking National Environmental Stewardship; Yale Center for Environmental Law & Policy: New Haven, CT, USA, 2005.
19.Food and Agriculture Organization (FAO). Guidelines: Land evaluation for Rainfed Agriculture; FAO Soils Bulletin No. 52; FAO: Rome, Italy, 1983.
20.Gumindoga, W., Makurira, H. and Garedondo, B., Impacts of landcover changes on streamflows in the Middle Zambezi Catchment within Zimbabwe. Proc. I.A.H.S., 2018, 378, 43-50.
21.Hannaford, J. and Buys, G., Trends in seasonal river flow regimes in the UK. J. Hydrol., 2012, 475, 158–174.
Hansen, J., Ruedy, R., Sato, M. and Lo, K., Global surface temperature change. Reviews of Geophysics, 2010, 48 (RG4004)
22.Hsu, H.H., Chen, C.T., Lu, M.M., Chen, Y.M., Chou, C. and Wu, Y.C., Climate change in Taiwan: Scientific Report 2011; National Science and Technology Center for Disaster Reduction: New Taipei, Taiwan, 2011.
23.Huang, J.C., Lee, T.Y. and Lee, J.Y., Observed magnified runoff response to rainfall intensification under global warming. Environ. Res. Lett., 2014, 9, 034008.
24.Isaacson, D.L. and Madsen, R., Markov Chains: Theory and Applications; Wiley: New York, NY, USA, 1976; p. 267.
25.Kahya, E. and Kalayci, S., Trend analysis of streamflow in Turkey. J. Hydrol., 2004, 289, 128–144.
26.Kendall, M.G., Rank Correlation Methods, Charles Griffin: London, UK, 1975.
27.Kisi, Ö., Santos, C.A.G., Silva, R.M. and Zounemat-Kermani, M., Trend analysis of monthly streamflows using Şen’s innovative trend method. Geofizika, 2018, 35(1).
28.Langat, P.K., Kumar, L. and Koech, R., Temporal Variability and Trends of Rainfall and Streamflow in Tana River Basin, Kenya. Sustainability, 2017, 9(11), 1963.
29.Liang, L. and Liu, Q., Streamflow sensitivity analysis to climate change for a large water-limited basin. Hydrol. Process., 2014, 28, 1767–1774.
30.Lins, H.F. and Slack, J.R., Streamflow trends in the United States. Geophys. Res. Lett., 1999, 26, 227–230.
31.Lohani, V.K. and Loganathan, G.V., An early warning system for drought management using the Palmer drought index. J. Am. Water Resources Assoc., 1997, 33, 1375–1386.
32.Lohani, V.K., Loganathan, G.V. and Mostaghimi, S., Long-term analysis and short-term forecasting of dry spells by the Palmer drought severity index. Nord. Hydrol., 1998, 29, 21–40.
33.Madadgar, S. and Moradkhani, H., Drought Analysis under Climate Change Using Copula. J. Hydrol. Eng., 2013, 18, 746–759.
34.Manikandan, M. and Tamilmani, D., Assessing hydrological drought charactertics: A case study in a sub basin of Tamil Nadu, India. Agric. Eng., 2015, 1, 71–83.
35.Mann, H.B., Non-parametric test against trend. Econometrica, 1945, 13, 245–259.
36.Marhaento, H., Booij, M.J. and Hoekstra, A.Y., Attribution of changes in stream flow to land use change and climate change in a mesoscale tropical catchment in Java, Indonesia. Hydrology Research, 2017, 48(4), 1143-1155.
37.McKee, T.B., Doeskin, N.J. and Kleist, J., The Relationship of Drought Frequency and Duration to Time Scales. In Proceedings of the Eighth Conference on Applied Climatology, Anaheim, CA, USA, 17–23 January 1993; American Meteorological Society: Boston, MA, USA, 1993; pp. 179–184.
38.Mishra, A.K., Amor, I.V.M., Das, N.N., Khedun, C.P., Singh, V.P., Sivakumar, B. and Hansen, J.W., Anatomy of a localscale drought: Application of assimilated remote sensing products, crop model, and statistical methods to an agricultural drought. J. Hydrol., 2015, 526, 15–29.
39.Mishra, A.K. and Singh, V.P., A review of drought concepts. J. Hydrol., 2010, 391, 202–216.
40.Mishra, A.K. and Singh, V.P., Drought modeling—A review. J. Hydrol., 2011, 403, 157–175.
41.Mishra, A.K., Singh, V.P. and Desai, V.R., Drought characterization: A probabilistic approach. Stoch. Environ. Res. Risk Assess., 2009, 23, 41–55.
42.Mulu, A., Fasnamol, T.M. and Dwarakish, G.S., Estimation of Changes in Annual Peak Flows in Netravathi River Basin, Karnataka, India. Climate Change Impacts, 2017, 82, 193-199.
43.Myronidis, D., Ioannou, K., Fotakis, D. and Dörflinger, G., Streamflow and Hydrological Drought Trend Analysis and Forecasting in Cyprus. Water Resources Management, 2017, 32(5), 1759-1776.
44.Nalbantis, I., Evaluation of a Hydrological Drought Index. Eur. Water, 2008, 23, 67–77.
45.Nalbantis, I. and Tsakiris, G., Assessment of hydrological drought revisited. Water Resources Manag., 2009, 23, 881–897.
46.Ngongondo, C.S., An analysis of long-term rainfall variability, trends and groundwater availability in the Mulunguzi river catchment area, Zomba mountain, Southern Malawi. Quat. Int., 2006, 148, 45–50.
47.Nicholls, R.J. and Cazenave, A., Sea-level rise and its impact on coastal zones. Science, 2010, 328, 1517–1520.
48.Nourani, V., Mehr, A.D. and Azad, N., Trend analysis of hydroclimatological variables in Urmia lake basin using hybrid wavelet Mann–Kendall and Şen tests. Environmental Earth Sciences, 2018, 77, 207.
49.Ochola, W.O. and Kerkides, P., A Markov chain simulation model for predicting critical wet and dry spells in Kenya: Analysing rainfall events in the Kano plains. Irrig. Drain., 2003, 52, 327–342.
50.O'Neil, H.C.L., Prowse, T.D., Bonsal, B.R. and Dibike, Y.B., Spatial and temporal characteristics in streamflow-related hydroclimatic variables over western Canada. Part 1: 1950–2010. Hydrology Research, 2017, 48(4), 915-931.
51.Palmer, W.C., Meteorological Drought; Research Paper No. 45; U.S. Department of Commerce, Weather Bureau: Washington, DC, USA, 1965; p. 58.
52.Palmer, W.C., Keeping track of crop moisture conditions, nationwide: The new Crop Moisture Index. Weatherwise, 1968, 21, 156–161.
53.Panu, U.S. and Sharma, T.C., Challenges in drought research: Some perspectives and future directions. Hydrol. Sci. J., 2002, 47, S19–S30.
54.Pasquini, A.I. and Depetris, P.J., Discharge trends and flow dynamics of South American rivers draining the southern Atlantic seaboard: An overview. J. Hydrol., 2007, 333, 385–399.
55.Paulo, A.A. and Pereira, L.S., Prediction of SPI drought class transitions using Markov chains. Water Resources Manag., 2007, 21, 1813–1827.
56.Petrow, T. and Merz, B., Trends in flood magnitude, frequency and seasonality in Germany in the period 1951–2002. J. Hydrol., 2009, 371, 129–141.
57.Pettit, A.N., A non-parametric approach to the change point problem. J. R. Stat. Soc. Ser. C, 1979, 28, 126–135.
58.Rouge, C., Ge, Y. and Cai, X., Detecting gradual and abrupt changes in hydrological records. Adv. Water Resour., 2013, 53, 33–44.
59.Sen, P.K., Estimates of the regression coefficient based on Kendall’s tau. J. Am. Stat. Assoc., 1968, 63, 1379–1389.
60.Shafer, B.A. and Dezman, L.E., Development of a Surface Water Supply Index (SWSI) to Assess the Severity of Drought Conditions in Snowpack Runoff Areas. In Proceedings of the Western Snow Conference, Fort Collins, CO, USA, 19–23 April 1982; pp. 164–175.
61.Sharma, T.C. and Panu, U.S., Analytical procedures for weekly hydrological droughts: A case of Canadian rivers. Hydrol. Sci. J., 2010, 55, 79–92.
62.Stojković, M., Kostić, S., Prohaska, S., Plavšić, J. and Tripković, V., A New Approach for Trend Assessment of Annual Streamflows: a Case Study of Hydropower Plants in Serbia. Water Resources Management, 2017, 31(4), 1089-1103.
63.Tabari, H., Nikbakht, J. and Talaee, P.H., Hydrological Drought Assessment in Northwestern Iran Based on Streamflow Drought Index (SDI). Water Resources Manag., 2013, 27, 137–151.
64.Tigkas, D., Vangelis, H. and Tsakiris, G., Drought and climatic change impact on streamflow in small watersheds. Sci. Total Environ., 2012, 440, 33–41.
65.Tosunoglu, F. and Kisi, Ö., Trend Analysis of Maximum Hydrologic Drought Variables Using Mann–Kendall and Şen's Innovative Trend Method. River Research and Applications, 2017, 33, 597-610.
66.Tsakiris, G. and Vangelis, H., Establishing a Drought Index Incorporating Evapotranspiration. Eur. Water, 2005, 9, 3–11.
67.UN Secretariat, General United Nations Convention to Combat Drought and Desertification in Countries Experiencing Serious Droughts and/or Desertification, Particularly in Africa. Available online: http://legal.un.org/avl/ha/unccd/unccd.html (accessed on 6 August 2015).
68.Water Resources Agency (WRA), Master Plan of Water Resources Management for Northern Taiwan; Ministry of Economic Affairs, WRA: Taipei, Taiwan, 2009.
69.Water Resources Agency (WRA). Hydrological Year Book of Taiwan; Ministry of Economic Affairs: Taipei, Taiwan, 2015.
70.Wilhite, D.A., Drought: A Global Assessment; Routledge Hazards and Disasters Series, Routledge: London, England, 2000.
71.Wilhite, D.A. and Glantz, M.H., Understanding the drought phenomenon: The role of definitions. Water Int., 1985, 10, 111–120.
72.Woli, P., Jones, J.W., Ingram, K.T. and Fraisse, C.W., Agricultural reference index for drought (ARID). Agron. J., 2012, 104, 287–300.
73.World Meteorological Organization (WMO). Report on Drought and Countries Affected by Drought During 1974–1985; WMO: Geneva, Switzerland, 1986; p. 118.
74.Xue, L., Yang, F., Yang, C., Chen, X., Zhang, L., Chi, Y. and Yang, G., Identification of potential impacts of climate change and anthropogenic activities on streamflow alterations in the Tarim River Basin, China. Scientific reports, 2017, 7, 8254.
75.Yang, J., Chang, J., Wang, Y., Li, Y., Hu, H., Chen, Y., Huang, Q. and Yao, J., Comprehensive drought characteristics analysis based on a nonlinear multivariate drought index. Journal of Hydrology, 2018, 557, 651-667.
76.Yevjevich, V., An Objective Approach to Definitions and Investigations of Continental Hydrologic Drought. Hydrology Paper No. 23; Colorado State University: Fort Collins, CO, USA, 1967.
77.Yu, P.S., Yand, T.C. and Kuo, C.C., Evaluating long-term trends in annual and seasonal precipitation in Taiwan. Water Resour. Manag., 2006, 20, 1007–2023.
78.Zamani, R., Mirabbasi, R., Abdollahi, S. and Jhajharia, D., Streamflow trend analysis by considering autocorrelation structure, long-term persistence, and Hurst coefficient in a semi-arid region of Iran. Theoretical and Applied Climatology, 2017, 129(1-2), 33-45.
79.Zamani, R., Tabari, H. and Willems, P., Extreme streamflow drought in the Karkheh river basin (Iran): Probabilistic and regional analyses. Nat. Hazards, 2015, 76, 327–346.
80.Zargar, A., Sadiq, R., Naser, B. and Khan, F.I., A review of drought indices, Environmental Reviews, 2011, 19, 333-349.
81.Zhang, X., Harvey, K.D., Hogg, W.D. and Yuzyk, T.R., Trends in Canadian streamflow. Water Resour. Res., 2001, 37, 987–998.