Decadal Changes of Rainfall and Temperature Extremes over the different Agro Economical Zones (AEZ) of Bangladesh

Transcription

1 Decadal Changes of Rainfall and Temperature Extremes over the different Agro Economical Zones (AEZ) of Bangladesh Professor A.K.M. Saiful Islam Md. Alfi Hasan Institute of Water and Flood Management Bangladesh University of Engineering and Technology (BUET)

2 Outline of the Presentation Past Climate: Changes of Extreme Climate over Bangladesh comparing the latest two decades ( ) with previous two decades ( ). Results are presented for the 34 Agro-ecological zones of Bangladesh. Future Climate : Changes of future extreme climate by using the multi-model ensemble simulations of A1B emission scenarios and new RCP emission scenarios over the CORDEX SA domain. Changes of Extreme Events - Droughts: Changes of meteorological, agricultural and combined droughts over Bangladesh.

3 Background According to the latest assessment report of IPCC (AR5 WG-I) climate change has profound impact on rainfall intensity and variability. The trend of extreme precipitation is increasing globally and consequently the heavy precipitation indices are increasing. Bangladesh is prone to natural disasters like cyclone, floods and droughts and vulnerable to climate change.

4 Collection of observed meteorological data from Bangladesh Meteorological Department Data of 28 stations out of 34 stations of BMD used in the study which passes homogeneity and consistency test. Data collected from BMD- Rainfall Maximum and Minimum Temperature Observed data has been divided into the following two time periods each 20 years to detect the changes Seasons: Winter (Dec-Feb) Pre monsoon (Mar-May) Monsoon (Jun-Sep) Post monsoon (Oct-Nov)

5 Percentage of Change (%) Percentage of Change (%) Inter-seasonal changes of temperature and rainfall in the past two decades Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Premonsoon Monsoon Postmonsoon Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Less Monsoon rainfall

6 Changes of Extreme climate A number of standard indicators are used to quantify changes of extreme climate which are listed below- Consecutive wet days, CWD Consecutive dry days, CDD Number of days when Rain > 100mm, RX100 Changes of Minimum temperature Changes of maximum temperature Changes of Diurnal ranges of temperature

7 Consecutive Dry Days Increased

8 PDF of CDD

9 Consecutive Wet Days Decreased

10 PDF of CWD

11 Number of rainy days when rainfall is more than 100mm Decreased

12 PDF of R100

13 Minimum temperature during December Increased

14 Maximum temperature during December Increased

15 Maximum temperature during April (summer) Increased

16 Results presented for the 31 Agro-Ecological Zones (AEZ) of Bangladesh Zones having the same Ecological Cropping pattern Soil Climate

17 Changes of maximum temperature for different AEZ during April Agro-ecological Zone Change Old Himalayan Piedmont Plain Active Tista Floodplain Tista Meander Floodplain Karatoya-Bangali Floodplain Lower Atrai Basin Lower Purnabhaba Floodplain Active Brahmaputra-Jamuna Floodplain Young Brahmaputra and Jamuna Floodplains Old Brahmaputra Floodplain Active Ganges Floodplain High Ganges River Floodplain Low Ganges River Floodplain Ganges Tidal Floodplain Gopalganj-Khulna Bils Arial Bil Middle Meghna River Floodplain Lower Meghna River Floodplain Young Meghna Estuarine Floodplain Old Meghna Estuarine Floodplain Eastern Surma-Kusiyara Floodplain Sylhet Basin Northern and Eastern Piedmont Plains Chittagong Coastal Plain Level Barind Tract High Barind Tract North-Eastern Barind Tract Madhupur Tract Northern and Eastern Hills Akhaura Terrace

18 Changes of extremes in the past decades It has been found that, consecutive wet days (CWD) are decreased almost uniformly all over Bangladesh from previous two decades period (from 1971 to 1990) to recent decades (from 1991 to 2010). Monsoon rainfall will be occurred in a shorter period and can cause crop damage. On the other hand, consecutive dry days (CDD) per year have increased rapidly around north western part of the country. This suggested the increase of drought in winter Rabi season over the country. Number of rainy day exceeding 20mm rain decreased rapidly in past decades in almost all parts of Bangladesh except the Chittagong Coastal. As Chittagong region is vulnerable to heavy rainfall and landslides, this increase of rainy day make the situation more adverse. Both Maximum and Minimum Temperature has been increase during winter and summer which can hamper winter crops.

19 Future Changes of Extremes using Predictions from Regional Climate Models

20 Future Changes of Climate Extremes using Multi-member simulations of PRECIS The Quantifying Uncertainty in Model Predictions (QUMP) research theme aims to provide probabilistic predictions of future climate. All these QUMP ensembles (total 17) simulations have conducted over Bangladesh to capture a wide range of probable future. High resolution 25km simulation can provide climate information to smaller regional administrative level.

21 QUMP ensembles (total 17) Ranges between AR4 multi-model ensembles

22 Daily rainfall (mm/day) Model Evaluation: Annual Cycle of Rainfall 18 Dry bias Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Qump0 Qump1 Qump2 Qump3 Qump4 Qump5 Qump6 Qump7 Qump8 Qump9 Qump10 Qump11 Qump12 Qump13 Qump14 Qump15 Qump16 Qump_All APH CRU GPCP Observe Model capture similar annual rainfall pattern for all the ensembles. Even, observational data sets are not similar to each other due to grid generation methodology.

23 Tempereture ( C) Model Evaluation: Annual Cycle of Temperature 35 Qump0 33 Qump1 31 Qump2 Qump3 29 Qump Warm bias Cold bias Qump5 Qump6 Qump7 Qump8 Qump Qump10 Qump11 Qump Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Qump13 Qump14 Qump15 Qump16 Qump_All Observe Temperature pattern adjust with model simulations. Spatial pattern also captured well by the model simulations.

24 2011 to to to 2100 Cahnge of annual rainfall (mm) Changes of Future Rainfall Three time slices have used : 2020s as short period ( ) 2050s as medium period ( ) 2080s as long period ( ) 1980s as baseline ( ) Increase of rainfall in Monsoon Decrease of rainfall in post monsoon

25 Inter-Seasonal Changes of Temperature 7.0 More increase More increase s 50s 80s s 50s 80s s 50s 80s s 50s 80s Winter Summer Monsoon Postmonsoon

26 Extreme Indices of Rainfall and Temperature Index Descriptive Name Units PRCPTOT wet day rainfall mm SDII simple daily intensity index mm/day CDD consecutive dry days days CWD consecutive wet days days R99p extremely wet day rainfall mm R95p very wet day rainfall mm SU25 hot days days TN90p hot night frequency % TX90p hot day frequency % TXx Max Tmax ºC TNn Min Tmin ºC DTR Diurnal temperature range ºC

27 CWD and CDD

28 PRTOT and SDII

29 R99P and R95P

30 TN99p

31 Changes of Extremes It has been found that both CDD and CWD days has been decreased. But total rainfall will increase. Hence, monsoon becomes more wetter and dry season becomes more drier. Chances of flooding has increased. Drier scenarios suggest rainfall will be lesser in South Western(SW) region. North eastern(ne) region experience more rainfall than any other parts of the country. Both maximum and minimum temperature has been increased during December which pose adverse impact on clod loving crops. Summer becomes more hotter than past.

32 Inter-annual changes of Rainfall from CMIP5 models over CORDEX domain

33 Inter-seasonal changes of rainfall from CMIP5 models over CORDEX domain Monsoon rain increase Winter rain decrease

34 Changes of Meteorological and Agricultural Droughts of Bangladesh

35 Droughts in Bangladesh Drought events have severe impact on country s agricultural economy in past years. Between 1960 and 1991, droughts occurred in Bangladesh 19 times. Very severe droughts hit the country in 1951, 1961, 1975, 1979, 1981, 1982, 1984, and 1989.

36 SPI based Drought Severity Index Standard Precipitation Index (SPI) for estimate meteorological droughts based on rainfall data Range Condition SPI -2 Extremely dry -2 < SPI -1.5 Severely dry -1.5 < SPI -1 Moderately dry -1 < SPI 1 Near normal 1 < SPI 1.5 Moderately wet 1.5 < SPI 2 Severely wet SPI 2 Extremely wet

37 Calculation of SPI 5 time period has considered to calculate SPI. 1- month (monthly SPI) 3- month (Seasonal SPI) 6-month (Short time SPI) 9 month (Medium time SPI) 12 month (Long term SPI) SPI is calculated both temporally and spatially.

38 Number of extreme drought events during and Increased 3-month SPI Extreme Droughts during Rabi season

39 Number of severe drought events during and Increased 3-month SPI Severe Droughts during Rabi season

40 Number of moderate drought events during and Increased 3-month SPI Moderate Droughts during Rabi season

41 Changes of drought severity Seasonal SPI or 3-month SPI is useful to understand the soil moisture condition of an area. Considering 3-month SPI it has found that, frequency of sever and moderate drought increased in the north western part of Bangladesh. Using SPI-6 month, long term seasonal extreme drought increased rapidly from 1980s to 2000s time period, especially over entire north-western region of Bangladesh.

42 Challenges to Identify Droughts using only meteorological data For tropical country with high intensive rainfall indentify drought index is a challenging task. A new types of drought indicator has been proposed by AghaKouchak (2013) which can incorporate precipitation and soil moisture. Multivariate Standardized Drought Index (MSDI) will be use be useful tool for indentifying current and future droughts over Bangladesh.

43 Combined Drought Index SPI (Standard Precipitation Index ) Derived from observed rainfall station data. MSDI (Multivariate Multi- Index Drought) Combined Drought indicator SSI (Standard Saturation Index ) Derived from satellite soil moisture data.

44 SPI (Standard Precipitation Index ) Only SPI is not able to capture droughts of 1982

45 SSI (Standard Soil Moisture Index ) SSI is able to capture droughts of 1982

46 SSI (Standard Soil Moisture Index ) Similar Criteria of drought identification has been used in analyzing SSI Index. Monthly SSI value are analyzed in suitable probability distribution and quartiles are analyzed for each cell over Bangladesh. Range SSI -2 Condition Extremely dry -2 < SSI -1.5 Severely dry -1.5 < SSI -1 Moderately dry -1 < SSI 1 Near normal 1 < SSI 1.5 Moderately wet 1.5 < SSI 2 Severely wet SSI 2 Extremely wet

47 Soil Moisture data Satellite based soil moisture data availibility: ECV Soil Moisture data : 1979 to 2010 (25km resolution) L3 Soil Moisture data : 2010 to 2012 (50 km resolution) AMSR-E/Aqua L2B Surface Soil Moisture, Ancillary Parms, & QC EASE-Grids : 2003 to present (25 km resolution)

48 Decadal changes of Soil Moisture Index SMI in 1990s (left) and 2000s (right) Stress Increased

49 Thank you On-going research projects on Extreme climate in BUET: HELIX (High End Climate Impact and Extremes) funded by EU, AFACI funded- Productions of Agro-meteorological Information for the Adaptation to Climate Change in Bangladesh F-FLOOD (Flash Flood Forecasting for the North East Regions of Bangladesh) funded by IFAD, COMSATS (Characteristics and Mechanism of Climate Extremes in the Context of Climate Change).