Calibration of PRECIS in employing future scenarios in Bangladesh

Abstract

Providing Regional Climates for Impacts Studies (PRECIS) is a regional climate model, which is used for the simulation of regional-scale climatology at high resolution (i.e. 50-km horizontal resolution). The calibration of rainfall and temperature simulated by PRECIS is performed in Bangladesh with the surface observational data from the Bangladesh Meteorological Department (BMD) for the period . The Climate Research Unit (CRU) data is also used for understanding the performance of the model. The results for the period 1961-1990 are used as a reference to find the variation of PRECIS-projected rainfall and temperature in 2071, in and around Bangladesh, as an example. Analyses are performed using the following two methods: (1) grid-to-grid and (2) point-to-point analyses. It is found that grid-to-grid analysis provides overestimation of PRECIS in Bangladesh because of downscaling of observed data when gridded from asymmetric low-density data network of BMD. On the other hand, model data extracted at observational sites provide better performance of PRECIS. The model overestimates rainfall in dry and pre-monsoon periods, whereas it underestimates it in the monsoon period. Overall, PRECIS is found to be able to estimate about 92% of surface rainfall. Model performance in estimating rainfall increases substantially with the increase in the length of time series of datasets. Systematic cold bias is found in simulating the annual scale of the surface temperature. In the annual scale, the model underestimates temperature of about 0.61°C that varies within a range of +1.45°C to −3.89°C in different months. This analysis reveals that rainfall and temperature will be increased in Bangladesh in 2071. On the basis of the analyses, look-up tables for rainfall and temperature were prepared in a bid to calibrate PRECIS simulation results for Bangladesh. The look-up tables proposed in this analysis can be employed in the application of the projected rainfall and temperature in different sectors of the country. These look-up tables are useful only for the calibration of PRECIS simulation results for future climate projection for Bangladesh.

Rainfall and Temperature Scenario for Bangladesh

“…Model overestimated pre-monsoon rainfall and underestimated monsoon rainfall with amounts in post-monsoon and dry periods is almost closer. The similar result is reported by Islam et al [17]. To find an adjustment between model and observed rainfall amounts the following regression equation is proposed: RF estimated = constant + slope RF scenario (1) where RF estimated is the rainfall to be projected and RF scenario is the PRECIS simulated rainfall scenario.…”

“…TRMM derived rainfall can be considered as the ground-truth amount even it scans from the upper side of the convective systems. The TRMM measured rainfall is already calibrated with ground-based rain-gauge rainfall in Bangladesh (Islam and Uyeda [17]). It is found that TRMM is able to catch about 97% of the surface rain.…”

“…For the application of PRECIS for climate change impact studies in Bangladesh, it is important to find out the appropriate calibration method. Having this in mind, analyses have been performed on point-to-point basis [17]. In this procedure, observed data at a particular site is considered as the representative of that location.…”

Climate change projections for the tropical Andes using a regional climate model: Temperature and precipitation simulations for the end of the 21st century

“…The regional model includes 19 vertical levels from the surface to approximately 30 km in the stratosphere and solves a hydrostatic version of the full primitive equations on a spherical‐polar grid [ Jones et al , 2004]. PRECIS has been successfully applied in previous studies to assess future changes in precipitation and cloud formation in Costa Rica [ Karmalkar et al , 2008], changes in coastal wind strength off the west coast of South America [ Garreaud and Falvey , 2008], extreme events in China [ Zhang et al , 2006] and climate in Bangladesh [ Nazrul Islam et al , 2008].…”

A Change of Climate Provokes a Change of Paradigm: Taking Leave of Two Tacit Assumptions about Physical Lake Forcing

“…Almost without exception, these studies show ice-on occurring progressively later in the year and ice-off progressively earlier in the year, resulting in a general decrease in the duration of lake ice cover and a corresponding increase in the duration of the ice-free season. In an analysis of the history of the occurrence of ice cover on eleven Swiss lakes that do not freeze over every winter, HENDRICKS FRANSSEN and SCHERRER (2008) showed that the frequency of occurrence of ice cover has decreased substantially over the past 40 years.…”