CLIMATE SCIENCE FOR SERVICE PARTNERSHIP CHINA

SEASONAL FORECASTS FOR THE YANGTZE RIVER BASIN

UNDERSTANDING AND WARNING OF EXTREME RAINFALL AND FLOODING

Extreme climatic events, such as intense rainfall and drought, can have serious impacts on society, including the loss of lives and livelihoods. Improving understanding, prediction and advice on extreme events in China is a core theme of CSSP China, and has already generated new advances based on the latest science.

What CSSP China is doing

To support climate-smart decision-making, CSSP China is developing the cutting-edge science needed to better understand and forecast extreme events such as flooding and drought in China.

The Yangtze river basin is home to one third of China’s population, covers one fifth of the land area, and includes many major cities and economic centres. In addition, the rural land that makes up most of the area is responsible for producing a vast amount of China’s agricultural yield.

However, the Yangtze river is affected by monsoon rainfall. The strength of the monsoon, and the time of year when it begins and ends, can have a large impact on livelihoods in the region. Particularly intense or prolonged periods of rainfall can lead to flooding and loss of life. In addition, hydroelectric dams along the river rely on the seasonal rainfall to produce electricity for the major cities of eastern and southern China.

By controlling the river water level, managers of hydroelectric dams are able to alleviate flood and drought impacts and regulate electricity supply. Finding out in advance how much rainfall there will be over the next few months, and particularly for the summer rainy season, is vital to supporting these activities.

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Climate Science for Service Partnership China 3

Seasonal prediction of rainfall – understanding the large scale causes

Research by scientists from China and the UK working on CSSP China1 found that the seasonal forecast system used by the Met Office has significant skill in predicting summer rainfall and natural river flow in the Yangtze river basin. They confirmed that this skill is linked to the model’s representation of the El Niño Southern Oscillation, and the way that El Niño in particular affects the monsoon in this part of China. In many cases, an El Niño during the winter season is followed by elevated risk of flooding along the Yangtze river in the following summer. This was the case for the devastating floods of 1998.

The climate system is complex so this pattern is not observed in every year following an El Niño, and in some years, El Niño and La Niña are inactive. There is also fundamentally unpredictable variability in the climate system so the most likely outcome from the seasonal forecast is not guaranteed. Scientists in the CSSP China project are working to ensure the statistical reliability of the risk based forecasts.

Collaborating to develop a prototype climate service

Summer rainfall, 2016

From the beginning of the CSSP China collaboration, managers of the hydroelectric dams in the Yangtze river basin have voiced a clear need for skilful forecasts of rainfall on seasonal timescales, particularly for the summer flood season. In 2015, CSSP China climate scientists recognised that there was a clear opportunity to make an important summer rainfall prediction for the Yangtze river basin for summer 2016, as long range forecasts were suggesting a very large El Niño event was on the way.

1 Li et al. 2016. Skillful seasonal prediction of Yang-tze river valley summer rainfall. Environmental Re-search Letters. http://iopscience.iop.org/arti-cle/10.1088/1748-9326/11/9/094002

A prototype climate service was therefore trialled, with scientists at the Met Office producing a real-time seasonal forecast for the Yangtze river basin throughout the spring and summer of 2016. The forecast was delivered to key decision makers by the China Meteorological Administration and its regional centre, the Wuhan Regional Climate Centre. By working closely with decision makers, the trial helped provide appropriate interpretation of the uncertainty in the forecasts, and assisted robust decision-making. The forecast presented each month gave headline messages for the coming season including probabilities of above average rainfall and river flow. It also included a more detailed description and graphics outlining how the forecasts and their uncertainties relate to conditions in the past.

Associated with the strong El Niño, the early summer precipitation forecasts predicted high likelihood of above-average rainfall in the Yangtze river basin, as well as above-average river flow. Operators of the large hydroelectric dams were able to make more confident decisions to prepare for higher river flow and potentially avoid costs to life, livelihoods and infrastructure.

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UK-China Research Innovation Partnership Fund information

The Weather and Climate Science for Service Partnership Programme – of which CSSP China is a part - comprises projects to develop partnerships harnessing UK scientific expertise to build the basis for strengthening the resilience of vulnerable communities to weather and climate variability, supported by the UK government’s Newton Fund.

For more information visit: www.newtonfund.ac.uk and follow via Twitter: @NewtonFund

For more information about CSSP China please visit the Met Office (www.metoffice.gov.uk/research/collaboration/cssp-china), IAP (www.lasg.ac.cn/cssp) or CMA (www.cma.gov.cn/en2014) or contact cssp-china@metoffice.gov.uk

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What’s next?

This prototype climate service is the first of several that are planned in CSSP China to address challenges posed to society by the climate, both in the short and longer term.

Work to evaluate the forecasts and service provided will help understand how to improve future climate services. Scientists continue to engage with decision makers to provide a seasonal forecast that better meets the needs of the people making decisions.

CSSP China is also working to develop climate service prototypes for sectors needing similar information on seasonal timescales, and those making decisions on longer timescales where climate change may begin to have an impact.

气候科学支持服务伙伴关系中国项目

中国长江流域的季节性预测

对极端降水和洪灾的了解和预警

集中降水和干旱等极端气候事件可能给社会带来严重影响，包括人员伤亡和生计损失。

增进和加强对中国极端气候事件的了解、预测和建议是CSSP中国项目的一项核心主题，并且已依托最新科学成果取得了新的进步。

CSSP中国项目正在进行的工作

为了支持实现气候智能型决策，CSSP中国项目正在开发必要的先进科学技术，以更好地了解和预测中国的洪灾和干旱等极端事件。

中国长江流域承载着中国三分之一的人口，占中国国土面积的五分之一，集中了众多主要城市和经济中心。此外，该区域占比最多的是农村土地，其产量在中国农业总产量中占有巨大份额。

然而，长江深受季风降水的影响，季风的强度和每年季风的起止时间都会对该地区民众的生计产生很大影响。高度集中或长时间的降水可导致洪灾和人员伤亡。同时，长江流域的水电站需要季节性降水来发电，为中国东部和南方的主要城市供应电力。

通过控制河流水位，水电站的管理者能够缓解洪水和干旱造成的影响，并能够调节电力供应。提前了解未来几个月的降水量，尤其是夏季多雨季节的降水量，对于支持此类活动至关重要。

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Climate Science for Service Partnership China 3

对降水的季节性预测——了解较大尺度的原因

CSSP中国项目中英双方科学家通过研究工作1 发现，英国气象局使用的季节性预测体系对于预测长江流域夏季降水和天然河流径流可发挥重要作用。他们确认，此技能与该模型对厄尔尼诺南方涛动现象的表征有关以及与厄尔尼诺现象本身对中国该区域季风产生影响的方式有关。在多个案例中，在冬季出现厄尔尼诺现象后，长江流域在次年夏季发生洪灾的风险都会升高。1998年的特大洪灾情况就是如此。

气候系统非常复杂，因此并非厄尔尼诺现象出现后的每一年都会有这种局面，而且在某些年份，厄尔尼诺和拉尼娜现象都不会出现。此外，气候系统中还存在根本无法预测的变率，因此季节性预测最有可能的结果并不一定会发生。CSSP中国项目的科学家正努力确保基于风险的预测在统计上具有可靠性。

通过协作开发气候服务原型2016年夏季降水

自CSSP中国项目协作启动以来，长江流域水电站的管理者都曾表达了对季节性降水有效预测的明确需求，尤其是对夏季汛期的。2015年，CSSP中国项目的气候科学家发现，由于长期预测表明一次非常大规模的厄尔尼诺事件即将出现，因此对2016年夏季长江流域进行重要的夏季降水预测迎来了一次极好的机会。

一项气候服务的原型因此进行了试验，由英国气象局的科学家针对长江流域开展了2016年春季和夏季的实时季节性预测。预测结果由中国气象局及其区域中心 - 武汉区域气候中心交付给了主要决策者。通过与决策者密切合作，该试验帮助对预测中的不确定性进行了恰当的解读，并帮助实现了可靠的决策。每月提交的预测针对即将到来的季节提供了重要信息，包括降水和河水流量高于平均水平的概率。预测还包括更为详尽的描述和图表，阐述了预测信息及其不确定性与以往条件的关联。

通过与强厄尔尼诺现象相联系，对夏初降水所作的预测表明长江流域有较高可能性出现高于平均水平的降水，此外河水流量也将高于平均水平。大型水电站的运营者得以在决策时更有信心，为河水流量的增加做好了准备，从而避免了对生命、生计和基础设施可能造成的损失。

1 Li等人。2016年。对长江流域夏季降水的有效季节性预测。Environmental Research Letters（《环境研究快报》）。http://iopscience.iop.org/arti-cle/10.1088/1748-9326/11/9/094002

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中英研究与创新合作基金信息

天气气候科学支持服务伙伴关系计划（CSSP中国项目是其中之一）包含多个伙伴关系项目，旨在依托英国政府牛顿基金（Newton Fund）的支持，利用英国的科学专长，为加强易受天气和气候变率影响社区的复原力提供基础。

如需更多信息，请访问：www.newtonfund.ac.uk，并通过Twitter关注：@NewtonFund

如需有关CSSP中国项目的更多信息，请访问英国气象局 (www.metoffice.gov.uk/research/collaboration/cssp-china)、IAP (www.lasg.ac.cn/cssp) 或CMA (www.cma.gov.cn/en2014) 网站，或联系cssp-china@metoffice.gov.uk

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下一步？

此项气候服务原型是CSSP中国项目规划的若干服务中的第一项；这些服务将有助于社会更好地应对在短期和更长期内所面临的气候挑战。

评估所提供预测和服务的工作将有助于理解如何改进将来的气候服务。科学家会继续与决策者保持联系，提供季节性预测，更好地满足决策者的需要。

CSSP中国项目还面向对季节性信息存在类似需求的行业以及面向就气候变化可能开始产生的更长时间尺度的影响进行决策的人士，开发各种气候服务原型。