Status:Ongoing analysis Material from: Linus, Ivan
1. Impact
Pakistan was devastated by widespread floods in end of August 2022. Since the beginning of the monsoon season in June a third of the country has been badly affected by floods that have killed more than 1000 people and displaced 33 million. There are several important aspect that have caused these devastating floods, such as melting glaciers, an active monsoon season and a week of widespread intense rainfall.
https://floodlist.com/asia/pakistan-floods-update-august-2022
2. Description of the event
An episode of torrential rain affected Pakistan around 21-26 August. The first plots below shows precipitation totals between 21 and 25 August from on STVL. The largest amounts were measured again in SE of Pakistan in Sindh province – over 200 mm which fell for about 2 to 3 days; these amounts look quite extreme compared to the model climate. Significants amounts of rain fell in many other parts of the country as well.
Looking at the CPC gauge-based gridded product reveals that heavy rain affected Sindh province and some areas in the NE on 23 August. This wet episode continued between 24 and 26 August moving eastwards. The estimates based on the data in our STVL database and also from CPC rainfall product shows that between 22 and 27 August in some places of SE and NW of Pakistan between 200 and 300 mm fell over already saturated ground – note that most of these amounts fell in much shorter period of time – a day or two.
The plots below show concatenated 6-hour forecasts from HRES for the period 23 August 00UTC to 26 August 00UTC. The two boxes represents a southern region and a northern region that will be evaluated in the forecast evolution plots below.
3. Predictability
3.1 Data assimilation
3.2 HRES
3.3 ENS
The plots below show EFI for 3-day precipitation 23-25 August. The outlined box is the southern box used below.
The plot below shows the forecast evolution plot for 72-hour precipitation valid 23 August 00UTC - 26 August 00UTC for the southern box. Concatenated 6-hour forecasts - green dot, HRES –red, ENS CF - purple, ENS blue box-and-whisker, Model climate – red box-and-whisker. Triangle marks the maximum in the model climate based on 1200 forecasts. In the distributions the black square represents the median and diamond ensemble mean.
The plot below is the same as above but for the northern box.
Compared to the model climatology, the event was more extreme in the northern box, even if the absolute magnitude was less. For this 3-day period (23-25 Aug), the forecast for the southern box from around 12 August started to pick up the risk of a wet period, but the really strong signal appeared only 1-2 days before the event started. For the northern box, the signal increase more gradually since 11 August.
3.4 Monthly forecasts
The panels in the plot below show extended-range EFI/SOT valid for the week 22-29 August.
The plot below shows the weekly average precipitation in a box covering NW. India and Pakistan for summer 2022, in ERA5 and extended-range ensemble mean forecasts with different lead times valid for the same week. Also week 6 forecasts predicted on average a wetter-than-normal season, but only from week 2-3 and shorter the forecast captured the intra-seasonal variability.
3.5 Comparison with other centres
3.6 EFAS/GLOFAS
The plots below show GLOFAS output before the onset (20 August) of the floods (left) and after (29 August) the event (right). In the right plot the bottom panel is for the same point as in the left plot.
