According to the research report by World Bank and Organization for Economic Co-operation and Development (OECD), the coastal cities on the globe are facing floods risks caused by descending surface and escalating sea level due to climate change. However, the current measures are not able to cope with itIf no urgent actions are taken by risky cities, they will suffer a total loss of 1 trillion dollars per year by 2050. In view of a growing population and assets, as predicted, flood damage would multiply in the coming decades, from $6 billion per city in 2005 to $52 billion in 2050 on average. Generally, the top 10 risky cities are Guangzhou, Miami, New York, New Orleans, Mumbai, Nagoya, Tampa, Boston, Shenzhen and Osaka.
It is crucial and imperative to establish a flood risk evaluation system, to interpret the possibility, activity level, damages and loses as well as impacts and harms of the disaster in a given region and period.
Disaster Warning and Evaluation Based on Remote Sensing (RS) Imagery
With space-covering and dynamic superiorities, the RS technique is unrivaled in aspects like disaster warning, monitoring, decision-making, assessing, reestablishing, etc. A large-scale, all-weather and all-time dynamic monitoring, quick response and accurate assessment are made possible by virtue of RS satellite data. A disaster risk evaluation assisted by RS would be more conducive in guiding relief work and reducing the damages.
The risk evaluation of the Songyuan City is carried out by analyzing indexes of 4 categories: causes, inducing environment, hazard-affected body and disaster prevention and alleviation capabilities.
（1）Disaster causes: or impetus factors of a flood. The leading factor of a rainstorm flood is rainstorms. In this context, the cause is mainly consisted of rainfall data.
From the above figure, a small rainfall can be seen in the Changling and Fuyu Counties in northeast and northwest of the Songyuan City respectively; an even less in the Qian’an and Ningjiang Counties; the most rainfall can be seen in the Qian Gorlos Mongol Autonomous County.
（2）Inducing environment: referring to the natural conditions of the underlying surface, which is relatively stable and helps to reallocate flood water. For example, the terrain influences regional drainage and confluences while vegetation could lock water and soil.
(3) Hazard-affected body: generally referring to the social and economic status such as the population and properties may be involved. When the population and property is more concentrated, the underlying damage and risk is higher.
(4) Disaster prevention and alleviation capabilities: referring to serial actions taken to cope with a flood disaster, e.g., hospital aids. The factor is largely decided by the local governmental economic support and the economic developmental level.
The average population, GDP and cultivated land proportion indexes are taken for assessment.
(1) The Changling and Fuyu counties and the Qian Gorlos Mongol Autonomous County have a higher disaster prevention and alleviation indexes; while the Qian’an and Ningjiang Counties are the lowest.
Risk Distribution of Rainstorm Floods in Songyuan City
（2）The Qian’anCounty, Nningjiang district and the coastal area along the Songhua River are at high risks;
(3) The northern Qian Gorlos Mongol Autonomous County and small parts of the eastern Changling County are at medium-high risks;
(4) The Fuyu and Changling Counties are at low or relatively low risks.
We Can Do More
（1）Warning and Monitoring of Post-Disaster Concurrent
We use RS imagery data and rainfall data from meteorological departments to analyze and forecast water levels, peak discharges and timing, taking account of reservoirs and lakes’ water storage and water absorption of soil. During the disaster, using RS imagery to extract data of the hazard-affected body is the premise of making disaster-relief plans and assessing damages and loses.
(2) Disaster Relief
By combining the RS data detected when floods occur and the GIS (Geographic Information System) technique, we can provide an optimized relief route, sufficient and accurate data for the relief work and scientific basis for the disaster alleviation in a quick manner. According to the images, we can locate the affected regions and the possible landslides and debris flows and work out an optimized rescue route.
(3) Estimation of Damages and Loses
We are able to make an overall evaluation of the damages & loses and the living conditions of the affected residents according to the historical and real-time RS data and field survey data, providing supports for re-construction and relief plans. GIS(Geographic Information System) comprehensive analysis and statistical analysis are utilized to detect the stricken areas, large-scale disaster situation, and damage degree; make detailed assessment of the loses of cultivated lands, forest lands, residential areas and industrial and mining sites; provide formed pictures, statistics and charts for relief guidance.