Currently, climate variability is becoming evident. Worldwide, mankind has faced extreme weather events such as severe floods, drought, sea level changes, glacier avalanches, and the reduction of the ice caps. This presentation shows the global trend in climate in general and the consequences on flood hazards in particular. First, historical data and trends in the global climate are presented. Some climate change scenarios by Intergovernmental Panel on Climate Change (IPCC) and their consequences are presented. Comparison of observed continental- and global-scale changes in surface temperature with results simulated by climate models using natural and anthropogenic forcings are presented. Decadal averages of observations are shown for the period 1906 to 2005 (IPCC, 2007: Summary for Policymakers. In Climate Change 2007). Other climate change scenarios are developed from Hadley Centre climate simulations (HadCM2 and HadCM3) and simulate global flows at a spatial resolution of 0.5^ox0.5^o using a macro-scale hydrological model (Arnell, 1999). The results show the expected change in the average annual runoff worldwide. The presentation covers flood modeling techniques (from simple to sophisticated) used for flood hazard assessment and the crucial role of GIS and its software in interpreting the results. An approach for incorporating climate change in hydrological models is presented in KSA.