performance of wrf (arw) over river basins in odisha, india during flood season 2014
DESCRIPTION
Operational Weather Research & Forecasting – Advanced Research WRF in short WRF (ARW) 9 km x 9 km Model (IMD)based rainfall forecast of India Meteorological Department (IMD) is utilized to compute rainfall forecast over River basins inOdisha during Flood season 2014. The performance of the WRF Model at the sub-basin level is studied in detail. It is observedthat the IMD’s WRF (ARW) day1, day2, day3 correct forecast range lies in between 31-47 %, 37-43%, and 28-47% respectivelyduring the flood season 2014.TRANSCRIPT
IJIRST –International Journal for Innovative Research in Science & Technology| Volume 2 | Issue 06 | November 2015 ISSN (online): 2349-6010
All rights reserved by www.ijirst.org 83
Performance of WRF (ARW) over River Basins in
Odisha, India During Flood Season 2014
Sumant Kr. Diwakar Dr. (Mrs.) Surinder Kaur
India Meteorological Department, New Delhi, India India Meteorological Department, New Delhi, India
Dr. Ashok Kumar Das Anuradha Agarwala
India Meteorological Department, New Delhi, India Faculty of Mathematical Sciences, Department of Statistics,
Delhi University
Abstract
Operational Weather Research & Forecasting – Advanced Research WRF in short WRF (ARW) 9 km x 9 km Model (IMD)
based rainfall forecast of India Meteorological Department (IMD) is utilized to compute rainfall forecast over River basins in
Odisha during Flood season 2014. The performance of the WRF Model at the sub-basin level is studied in detail. It is observed
that the IMD’s WRF (ARW) day1, day2, day3 correct forecast range lies in between 31-47 %, 37-43%, and 28-47% respectively
during the flood season 2014.
Keywords: GIS; WRF (ARW); IMD; Flood 2014; Odisha
_______________________________________________________________________________________________________
I. INTRODUCTION
Forecast during the monsoon season river sub-basin wise in India is difficult task for meteorologist to give rainfall forecast
where the country have large spatial and temporal variations. India Meteorological Department (IMD) through its Flood
Meteorological Offices (FMO) is issuing Quantitative Precipitation Forecast (QPF) sub-basin wise for all Flood prone river
basins in India (IMD, 1994). There are 10 FMOs all over India spread in the flood prone river basins and FMO Bhubaneswar,
Odisha is one of them. The Categories in which QPF are issued are as follows
Rainfall (in mm) 0 1-10 11-25 26-50 51-100 >100
Odisha is an Indian state on the subcontinent’s east coast, by the Bay of Bengal. It is located between the parallels of 17.49’ N
and 22.34’ N Latitudes and meridians of 81.27’ E and 87.29’ E Longitudes. It is surrounded by the Indian states of West Benga l
to the north-east and in the east, Jharkhand to the north, Chhattisgarh to the west and north-west and Andhra Pradesh to the
south. Bhubaneswar is the capital of Odisha.
Odisha is the 9th
largest state by area in India and the 11th
largest by population. Odisha has a coastline about 480 km long.
The narrow, level coastal strip including the Mahanadi river delta supports the bulk of the population. On the basis of
homogeneity, continuity and physiographical characteristics, Odisha has been divided into five major morphological regions.
The Odisha Coastal Plain in the east, the Middle Mountainous and Highlands Region, the Central Plateaus, the western rolling
uplands and the major flood plains.
River System A.
The river system of Odisha comprises the Mahanadi, Brahmani, Baitarani, Subarnarekha, Vamasadhara, Burhabalanga,
Rushikulya, Nagavali, Indravati, Kolab, Bahuda, Jambhira and other tributaries and distributaries. Table – 1
Major Rivers in Odisha with Catchment Area (Sq. Km)
Sl. No. Name of the Major River Basin Catchment Area (Sq. Km.)
% to Geographical area of State Total Area Within Odisha
1. Mahanadi 141134 65628 42.15
2. Brahmani 39116 22516 14.46
3. Baitarani 14218 13482 8.66
4. Kolab 20427 10300 6.61
5. Rushikulya 8963 8963 5.76
6. Vamsadhara 11377 8960 5.75
7. Indravati 41700 7400 4.75
8. Burhabalanga & Jambhira 6691 6354 4.08
9. Nagavali 9275 4500 2.89
10. Subarnarekha 19277 2983 1.92
11. Bahuda 1118 890 0.57
Performance of WRF (ARW) over River Basins in Odisha, India During Flood Season 2014 (IJIRST/ Volume 2 / Issue 06/ 015)
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Fig. 1: Location map of study Area
FMOs mainly using the synoptic analogue model to do the same which was developed by each FMO for the area of their
jurisdiction. But nowadays most of the countries tilted towards Numerical Weather Prediction (NWP) models as NWP methods
have achieved better skills and are playing important role in rainfall forecasting. Rainfall prediction skill of NWP model is still
not adequate to address satisfactorily detailed aspects of Indian Summer Monsoon. This is because of large spatial and temporal
variability of rainfall and some inherent limitations of NWP models. In-spite of these limitations rainfall forecast of NWP
models are estimated for its utilization in various fields such as in flood forecasting, water management, planning etc.
Operationally the WRF (ARW) 9 x 9 Km2 rainfall forecast is made available to Hydromet division by NWP division at New
Delhi and rainfall forecast estimation sub-basin wise for River basins is done by the Hydromet division at New Delhi using the
available data. Then this estimation forecast is uploaded in IMD website (www.imd.gov.in) operationally during flood season
2014 as an additional tool for issuing QPF for their sub-basins. This input in turn will be utilized in the flood forecasting purpose.
The main aim of this paper is to study the performance of WRF rainfall forecast during heavy rainfall events in the flood
season 2014 over river basins under Flood Meteorological Office, Bhubaneswar of IMD. The Figure 1 showing the location of
river sub basin map of the study Area.
Fig. 2: Rain-gauge Network
Performance of WRF (ARW) over River Basins in Odisha, India During Flood Season 2014 (IJIRST/ Volume 2 / Issue 06/ 015)
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II. Methodology
Sub basin wise rainfall forecast estimation for basins lying over the state of Odisha from operational WRF (9kmX9km) gridded
rainfall forecast is computed during the flood season. The meso-scale forecast system WRF (ARW) with 3DVAR data
assimilation is being operated daily twice, at 9 km horizontal resolutions with 38 Eta levels in the vertical and the integration and
with the outer model domain covers the area between lat. 25°S to 45°N long 40°E to 120°E for the forecast up to 3 days using
initial and boundary conditions from the IMD GFS-574/L64 (horizontal resolution over the tropics~22km)
(http://202.54.31.51/bias/aboutus.php). Following are the Physics options set to operational run of WRF viz. mp_physics-
WSM3(3), ra_lw_physics-rrtm scheme(1), ra_sw_physics- Dudhia scheme(1), bl_pbl_physics-YSU(1), cu_physics-GD
scheme(3). WRF (9kmx9km) gridded rainfall forecast data which is in netcdf format is averaged for each sub basins using
NCAR Command Language (NCL). Observed areal rainfall is computed by taking the average of station rainfall values lying in
each sub-basin. The correlation between the sub basin wise observed rainfall and the WRF model rainfall forecast rainfall (mm)
table is prepared for flood season 2014 and shown in Table 4. Daily rainfall bar graph over the basin areas is also prepared
during the Heavy Rainfall events over FMO Bhubaneswar to identify the dates in which the heavy rainfall occurred.
The performance of categorical QPF (0, 1-10 mm, 11-25 mm, 26-50 mm, 51-100 mm, > 100 mm) issued for sub basins is
verified from 6X6 categorically for different skill scores viz. Percentage of Correct (PC), Heidke Skill Score (HSS), Critical
Success Index (CSI) which is shown in Table 3 month-wise separately during Flood dates.
It is to be noted that due to technical issues the WRF Model did not run on 13 Aug, 14 Aug, 15 Aug and 4 Sep 2014, so
outputs are not available.
III. RESULTS AND DISCUSSION
The Rain-gauge network for real time reception of rainfall data in the basins over the Odisha during the flood season 2014 is
shown in figure 2. The total number of stations for real time rainfall data reception is 195. The summer monsoon rainfall over
Odisha occurs mostly due to monsoon depression, Low Pressure Systems (LPS) developing over the Bay of Bengal and moving
along the monsoon trough.
The dates of floods during the year 2014 are shown in the table below: Table – 2
Flood dates of 2014 in Odisha
Sl. No. Year Flood Dates
1.
2014
July 19-22 & July 27-30
2. Aug 01-17
3. Sep 01-09
July 2014 (Flood Period Are 19.07.2014 to 22.07.2014 & 27.07.2014 to 30.07.2014) A.
Synoptic Situation during the Flood Dates 1)
The Synoptic situation on 20.07.2014, a low pressure area (LOPAR) was formed over North Bay of Bengal and adjoining areas
of Gangetic West Bengal and Odisha with associated cyclonic circulation extends up to Mid tropospheric level. It was rapidly
concentrated into a Depression on 21st July 2014 over North Eastern parts of Odisha and adjoining areas of Gangetic West
Bengal about 50 km east of Baripada. On 22.07.2014, it was moved over North Chhattisgarh and neighborhood about 50 km
Southeast of Pendra. During this period, the axis of monsoon trough on mean sea level was passed through Ganganagar, Aligarh,
Fatehpur, Daltonganj, Midnapur and thence Southeast wards to East Central Bay of Bengal across North-west Bay of Bengal.
Performance of WRF (ARW) over River Basins in Odisha, India During Flood Season 2014 (IJIRST/ Volume 2 / Issue 06/ 015)
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Fig. 3: Daily Average Rainfall (mm) from 11 to 22 & 27 to 31 July 2014
On dated 27th
July 2014, a low pressure area (LOPAR) has formed over North West Bay of Bengal and neighborhood with
associated upper air cyclonic circulation extending up to Mid-Tropospheric level and continued up to dated 28th
July 2014. On
29th
July 2014, it was concentrated into a Well-Marked Low pressure area over the same region with associated upper air
cyclonic circulation extending up to Mid-Tropospheric level and continued up to 30th July 2014 over the same region. During the
period, the axis of monsoon trough on mean sea level passed through Anupgarh, Jaipur, Ambikapur, Sambalpur, centre of the
system and thence Southeast wards to East Central Bay of Bengal extending up to 1.5 km above sea level.
August 2014 (Flood period 03.08.2014 to 16.08.2014) B.
Synoptic Situation during the Flood Dates 1)
Monsoon was active on 03.08.14 and vigorous from 04.08.14 to 05.08.14 over Odisha. On 03.08.14, a low pressure area
(LOPAR) was formed over North Bay of Bengal and neighborhood with associated upper air cyclonic circulation extending up
to Mid-tropospheric level and became Well Marked Low pressure area over the same region in the evening.
On 04.08.14 it was intensified into a Depression over Gangetic West Bengal and neighborhood close to Midnapur and it became
Deep Depression in the same evening over Jharkhand and neighborhood.
On 05.08.14, it was moved over North Chhattisgarh, adjoining Jharkhand and East Madhya Pradesh about 100 km East-south-
east of Ambikapur. It was weakened into a Depression on 06.08.14 and further weakened into a Well-Marked Low (WML)
Pressure on 07.08.14 over North-West Madhya Pradesh and neighborhood. Under the influence of the cyclonic circulation over
North- Bay of Bengal and neighborhood on 08.08.14, a low pressure area was formed on 09.08.14 over the same region with
associated upper air cyclonic circulation extended up to Mid-Tropospheric level. It shifted over North Eastern part of Jharkhand
and neighborhood on 10.08.14 and then shifted over Southern parts of Bihar and neighborhood on 11.08.14 and it merged with
the monsoon trough on 12.08.14. However, associated upper air cyclonic circulation lied over East Uttar Pradesh and
neighborhood extending up to 4.5 KM above sea level and became less marked on 13.08.14.
Another upper air cyclonic circulation was over East Bihar and neighborhood extending up to Mid-tropospheric level on
13.08.14 shifted over Sub-Himalayan West Bengal and Sikkim and adjoining Bihar embedded with the trough on 14.08.14 and
continued up to 15.08.14. The axis of monsoon trough on mean sea level was present from Rajasthan to EC Bay of Bengal across
UP, Jharkhand GWB and Odisha from 03.08.2014 to 08.08.2014 and was from UP to East Central Bay of Bengal across Bihar,
Jharkhand and West Bengal from 09.08.2014 to 16.08.2014.
Performance of WRF (ARW) over River Basins in Odisha, India During Flood Season 2014 (IJIRST/ Volume 2 / Issue 06/ 015)
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Fig. 4: Daily Average Rainfall (mm) from 1 to 8 & 9 to 17 August 2014
September 2014 (Flood period 05.09.2014 to 08.09.2014) C.
Synoptic Situation during the Flood Dates 1)
South west monsoon was vigorous from 05.09.14 to 07.09.14 over Odisha. A Well-Marked Low (WML) pressure area over
North West Rajasthan and adjoining areas of Haryana and Punjab on 05.09.14 and became a low pressure area over Punjab and
adjoining Rajasthan and Haryana with associated cyclonic circulation extends up to 3.1 km above sea level on 06.09.14 and was
less marked on 07.09.14.
Another Low Pressure Area (LOPAR) was formed over North Bay of Bengal off West Bengal-Bangladesh coast on 05.09.14
with associated cyclonic circulation extends up to Mid Tropospheric level and it became WML over northwest Bay of Bengal
and adjoining Odisha-West Bengal coasts on 06.09.14 and shifted over Odisha and adjoining Chhattisgarh on 07.09.14 and on
08.09.14, it was over Southeast Madhya Pradesh and adjoining North Maharashtra with associated cyclonic circulation extends
up to Mid Tropospheric Level. The axis of monsoon trough on mean sea level was from West Rajasthan to East Central Bay of
Bengal across Uttar Pradesh, Bihar, Jharkhand, Odisha and North West Bay of Bengal throughout the period.
Fig. 5: Daily Average Rainfall (mm) from 1 to 9 to September 2014
Performance of WRF (ARW) over River Basins in Odisha, India During Flood Season 2014 (IJIRST/ Volume 2 / Issue 06/ 015)
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Comparison of Observed Rainfall with WRF Model Output on selected flood dates D.
Fig. 6: Comparison of 21st July 2015 Observed Rainfall with WRF Model Output
Performance of WRF (ARW) over River Basins in Odisha, India During Flood Season 2014 (IJIRST/ Volume 2 / Issue 06/ 015)
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Fig. 7: Comparison of 21st July 2015 Observed Rainfall with WRF Model Output
Performance of WRF (ARW) over River Basins in Odisha, India During Flood Season 2014 (IJIRST/ Volume 2 / Issue 06/ 015)
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Basin-Wise Comparison of Observed Rainfall with WRF Model Output for Some Dates E.
Fig. 8: Comparison of 31st July 2015 Observed Rainfall with WRF Model Output
Fig. 9: Comparison of 10th Aug. 2015 Observed Rainfall with WRF Model Output
Performance of WRF (ARW) over River Basins in Odisha, India During Flood Season 2014 (IJIRST/ Volume 2 / Issue 06/ 015)
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Fig. 10: Comparison of 7th Sep. 2015 Observed Rainfall with WRF Model Output
The performance of categorical QPF issued for river sub basins under FMO Bhubaneswar is verified by computing different
skill scores from 6 x 6 contingency table categorically viz., HSS, CSI, PC .There are no similar or nearby values found in PCs
from Day-1 to Day-3 for all the four events. Also some time PC value for day-2 forecast values is better than day-1, even PC
values decreases form day-3 to day-1. Therefore, rainfall forecast of WRF model during the events showed irregular behavior.
However, day-1 PC values lie between 31% to maximum 47%; day-2 PC values lie between 37% to 47% and day-3 PC values
lie between 28% to 47%.
Critical Success Index is decreasing for higher category of rainfall, which also stands that heavy rainfall events are not
correctly forecasted as compared to lower rainfall categories by the model. The HSS values are very low for all the events, even
low negative values are found. These stand that forecast accuracy is very low, even chance forecast is present. Table – 3
WRF Skill Scores of FMO Bhubaneswar for Flood season, 2014
WRF Skill Scores for FMO Bhubaneswar , 11 July - 31 July , 2014
Skill Score PC HSS CSI1 (0) CSI2 (1-10) CSI3 (11-25) CSI4 (26-50) CSI5 (51-100) CSI6 (>100)
Day-1 31.03 0.00 0.00 0.33 0.14 0.05 0.00 0.00
Day-2 37.24 0.06 0.05 0.33 0.22 0.13 0.00 0.00
Day-3 41.38 0.13 0.00 0.36 0.29 0.15 0.00 0.00
WRF Skill Scores for FMO Bhubaneswar , 1 August - 17 August , 2014
Skill Score PC HSS CSI1 (0) CSI2 (1-10) CSI3 (11-25) CSI4 (26-50) CSI5 (51-100) CSI6 (>100)
Day-1 46.51 0.05 0.00 0.46 0.19 0.00 0.00 0.00
Day-2 43.02 -0.03 0.00 0.41 0.15 0.00 0.00 0.00
Day-3 46.81 -0.01 0.00 0.51 0.06 0.00 0.00 0.00
WRF Skill Scores for FMO Bhubaneswar , 1 Sept -9 Sept , 2014
Skill Score PC HSS CSI1 (0) CSI2 (1-10) CSI3 (11-25) CSI4 (26-50) CSI5 (51-100) CSI6 (>100)
Day-1 43.08 0.16 0.00 0.34 0.27 0.24 0.00 -
Day-2 40.00 0.10 0.00 0.28 0.29 0.17 0.00 -
Day-3 27.69 -0.10 0.00 0.13 0.27 0.05 0.00 -
Table – 4
Correlation between WRF Model Output and Observed Rainfall
Correlation of Day1 Correlation of Day2 Correlation of Day3
Flood dates
Sub-basin
June
(20-
30)
July
(11-31)
Aug
(1-17)
Sep
(1-9)
June
(20-30)
July
(11-31)
Aug
(1-17)
Sep
(1-9)
June
(20-30)
July
(11-31)
Aug
(1-17)
Sep
(1-9)
Performance of WRF (ARW) over River Basins in Odisha, India During Flood Season 2014 (IJIRST/ Volume 2 / Issue 06/ 015)
All rights reserved by www.ijirst.org 92
Baitarani 0.33 0.46 0.00 0.64 0.21 0.28 0.75 0.45 -0.06 -0.06 0.46 -0.45
Brahmani 0.69 0.59 -0.04 0.70 0.85 0.34 0.47 0.78 0.42 0.11 0.70 -0.17
Burhabalanga 0.44 0.55 0.33 0.67 0.22 0.40 0.77 0.51 0.01 0.08 0.70 0.38
Lower Mahanadi 0.64 0.41 -0.40 0.61 0.70 -0.01 0.54 0.25 -0.02 0.21 -0.35 -0.33
Rushikulya 0.01 0.16 -0.02 0.40 0.23 -0.19 0.23 0.36 -0.20 -0.24 0.05 0.39
Subarnarekha 0.52 0.38 0.36 0.89 0.68 0.41 0.49 0.35 0.75 0.18 0.95 -0.25
Upper Mahanadi 0.88 0.65 0.02 0.06 0.71 0.34 0.17 0.31 0.35 0.36 0.42 -0.48
Vamsadhara -0.24 -0.25 -0.17 0.13 0.59 -0.10 -0.30 0.28 -0.23 -0.32 -0.42 0.00
Negative
Relation No Relation
Positive
Relation
The correlation table-4 clearly shows that there is mostly positive correlation between WRF model rainfall forecast and
observed rainfall which means that model prediction and observed rainfall have similar pattern. The WRF model forecast is
highly correlated with sub basin wise average observed rainfall for the sub-basins Subarnarekha, Burhabalanga, Upper Mahanadi
in most of the cases. However, very low or negative correlations are also found in many cases. Even few cases of no correlations
i.e. 0 values are also observed during the period.
This may be due to the large variation of rainfall in spatial as well as temporal distribution and inherent limitation of NWP
model.
IV. CONCLUSION
The heavy rainfall events are generally underestimated by WRF model rainfall during the study period. Critical Success Index is
decreasing for higher category of rainfall, which also stands that heavy rainfall events are not correctly forecasted by the model.
Low HSS value confirms that the WRF model rainfall forecast is not accurately predicted the heavy rainfall events. This may be
due to large spatial and temporal variability of rainfall and some inherent limitations of NWP models.
There are no similar or nearby values found in PCs from Day-1 to Day-3 for all the four events. Also some time PC value for
day-2 forecast values is better than day-1, even PC values decreases form day-3 to day-1. However, day-1 PC values lie between
31% to maximum 47%, day-2 PC values lie between 37% to 47% and day-3 PC values lie between 28% to 47%. Therefore,
rainfall forecast of WRF model during the events is showed irregular performance.
There is mostly positive correlation between WRF model rainfall and observed rainfall shows that model prediction and
observed rainfall have similar rainfall distribution over river basins. The WRF model forecast is highly correlated with sub basin
wise average observed rainfall for the sub-basins Subarnarekha, Burhabalanga, Upper Mahanadi in most of the cases. However,
very low or negative correlations are also found in some cases. Even few no correlations (i.e. 0 values) are also observed during
the period.
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