#72: Examining the Pakistan Floods of 2022 and Land Regeneration Strategies - Part-I
With an estimation on how much regeneration of land will be required to absorb rainfall and flood water in only one small area of Pakistan.
In #70, we discussed the Hunga Tunga eruption and its far-reaching impacts on global weather patterns, providing a backdrop to understanding how natural events can influence environmental conditions. Moving into #71, we explored hydrographs to analyze water flow and distribution in response to precipitation events. These discussions set the stage for our current focus on the Pakistan floods of 2022.
Background
Post 70: Hunga Tunga Eruption The Hunga Tunga eruption served as a stark reminder of the power of natural events to disrupt climatic and environmental systems. We examined how such events could lead to shifts in weather patterns, influencing rainfall and potentially contributing to extreme weather occurrences like floods.
Post 71: Hydrographs Analysis We delved into the concept of hydrographs, which track the flow of water in rivers and streams over time. This analysis is crucial for understanding how water moves through landscapes and can help predict the impact of heavy rainfall on flood-prone areas. By examining hydrographs, we can gain insights into the behavior of water during extreme weather events and the resulting flood risks.
Focus of Post 72
Building on these foundations, we now turn our attention to the Pakistan floods of 2022. This post will examine the most impacted zones through the lens of barrage flows and rainfall intensity, providing a comprehensive picture of the disaster. By utilizing various data sources, we aim to gain a clearer understanding of the extent of the damage and the areas most severely affected.
From there, I will outline a two-pronged approach to land regeneration. At the national level, we will discuss how much land each province needs to allocate to protect against future events of this magnitude. Specifically, we will look at the areas in districts of Larkana, Jacobabad, Ghotki in Sindh, one of the most flood-impacted regions. By enhancing infiltration rates up to and combining this with floodwater borewell recharge to further boost capacity to 610mm, we can transform designated barren areas, particularly targeting saline water zones to make them fertile again. However, in this first part, I am just aiming for a 60mm infiltration rate and corresponding regeneration area.
In-Depth Analysis of the 2022 Pakistan Floods
Overview of the Floods
The 2022 floods in Pakistan were among the most devastating in the country's history, primarily affecting the southern provinces of Sindh and Balochistan. The floods displaced over 33 million people and caused economic losses estimated at over $30 billion. The deluge was driven by a combination of extreme precipitation events and pre-existing high soil moisture conditions, exacerbated by atmospheric anomalies.
A: Meteorological and Hydrological Metrics
Extreme Precipitation and Atmospheric Rivers
Rainfall Metrics:
Total Rainfall: The southern provinces of Pakistan received unprecedented rainfall during July and August 2022. Sindh experienced over 726 mm of rain in August, which is more than five times the climatological average of approximately 145 mm for that month.
Peak Rainfall Events: The heaviest rainfall occurred between 16th and 25th August, with daily precipitation exceeding 90 mm on 18th August alone. This level of rainfall was well above the 99.9th percentile of the historical daily rainfall distribution for the region.
Cumulative Rainfall: Over the two months, the cumulative rainfall was about 900 mm, significantly higher than the 200 mm typical for this period, illustrating a 350% increase.
Atmospheric Rivers:
Two major atmospheric rivers passed over Pakistan during August 2022, contributing significantly to the extreme precipitation. These rivers transported moisture from the Arabian Sea, leading to prolonged and intense rainfall.
The atmospheric rivers were associated with integrated water vapor transport (IVT) intensities of more than 1,000 kg/m/s, categorizing them as strong atmospheric rivers capable of causing significant precipitation.
The presence of atmospheric rivers was a critical factor in the intensity and duration of rainfall, as these systems can carry vast amounts of moisture and release it over a concentrated area.
Soil Moisture and Runoff
Soil Moisture Levels:
Antecedent Soil Moisture: Prior to the rainfall events, the soil moisture in the affected areas was already high due to continuous rainfall in July. Soil moisture levels were measured at more than 90% of field capacity, which is above the 90th percentile of historical data.
Soil moisture data from NASA’s Level 3 Integrated Multi-satellite Retrievals for Global Precipitation Measurement (GPM) mission showed that soil moisture in the region was significantly higher than the average for the past two decades, contributing to the severity of runoff during the August floods.
Runoff and Streamflow:
Runoff Volumes: Hydrological models indicated that the runoff volumes during the peak of the floods were 300% higher than the historical average. For example, the streamflow at Kotri reached 25,000 cubic meters per second (m³/s) during the peak flooding, compared to a historical average of around 6,000 m³/s.
Streamflow Peaks: The peak streamflow exceeded the 99.9th percentile of annual maximum flows for the period 2001–2021. The models, which included Variable Infiltration Capacity (VIC), NOAH-MP, and Community Land Model (CLM), consistently showed extreme values during the flood event.
Hydrological Metrics
The Indus River and its tributaries saw dramatic increases in flow rates at various barrages during the flood peak, we are specifically looking at them because, the most damage occurred in the Indus river basin, there were other rivers which overflowed and flooded in Punjab, but there impact was limited. Here are the detailed metrics for each barrage along the Indus River, from upstream to downstream:
Tarbela Dam:
Normal Flow: Approximately 5,000 m³/s (176,573 cusecs).
Flood Peak: Approximately 10,000 m³/s (353,146 cusecs).
Reported Data (27.08.22): Inflow: 3,53,800 cusecs; Outflow: 3,74,900 cusecs.
Kalabagh Barrage:
Normal Flow: Approximately 6,000 m³/s (211,888 cusecs).
Flood Peak: Approximately 18,000 m³/s (635,664 cusecs).
Reported Data (27.08.22) : Inflow: 3,20,192 cusecs; Outflow: 3,16,192 cusecs.
Chashma Barrage:
Normal Flow: Approximately 7,000 m³/s (247,403 cusecs).
Flood Peak: Approximately 20,000 m³/s (705,960 cusecs).
Reported Data (27.08.22) : Inflow: 3,62,949 cusecs; Outflow: 3,83,257 cusecs.
Taunsa Barrage:
Normal Flow: Approximately 8,000 m³/s (282,883 cusecs).
Flood Peak: Approximately 22,000 m³/s (776,556 cusecs).
Reported Data (27.08.22) : 5,04,232 cusecs.
Guddu Barrage:
Normal Flow: Approximately 9,000 m³/s (317,966 cusecs).
Flood Peak: Approximately 25,000 m³/s (882,450 cusecs).
Reported Data (27.08.22): 5,05,000 cusecs.
Sukkur Barrage:
Normal Flow: Approximately 10,000 m³/s (352,699 cusecs).
Flood Peak: Approximately 27,000 m³/s (952,287 cusecs).
Reported Data (27.08.22) : 5,69,756 cusecs.
Kotri Barrage:
Normal Flow: Approximately 6,000 m³/s (211,888 cusecs).
Flood Peak: Approximately 25,000 m³/s (882,450 cusecs).
Reported Data (27.08.22): 3,15,279 cusecs.
Interpretation of Flow Data:
Taunsa vs. Guddu Barrage: During the flood event, the Taunsa Barrage handled an exceptionally high peak flow of approximately 504,232 cusecs. Downstream, the Guddu Barrage reported lower peak inflow rates around 505,000 cusecs, which suggests that a significant volume of floodwater was either infiltrated, stored, or diverted between Taunsa and Guddu. This discrepancy could be due to several factors:
Infiltration and Storage:
The landscape between Taunsa and Guddu may have facilitated the infiltration of floodwaters into the groundwater system. Wetlands, agricultural fields, and other permeable surfaces could have absorbed significant volumes of water.
Floodplain Management:
Floodplains between these barrages may have acted as natural buffers, distributing and temporarily storing floodwaters. Effective floodplain management can significantly reduce the volume of water reaching downstream areas.
Diversion Structures:
Possible existence of diversion canals or other infrastructure designed to manage excess water during flood events, reducing the burden on downstream barrages like Guddu.
These above metrics and observations provide some understanding of the hydrological and meteorological dynamics during the 2022 Pakistan floods, emphasizing the critical role of the Indus River basin in managing and mitigating flood impacts
B: Affected Areas and Impact
Geographical Extent:
Sindh and Balochistan: The provinces of Sindh and Balochistan were the most severely affected. Flood maps derived from Synthetic Aperture Radar (SAR) data showed that more than 160,000 square kilometers were inundated. Major cities like Sukkur, Larkana, and Hyderabad were heavily impacted.
Urban and Rural Impact:
Urban Areas: Cities experienced severe flooding due to inadequate drainage systems. For example, Karachi recorded over 200 mm of rainfall in a single day, overwhelming the city's drainage capacity.
Rural Areas: Extensive agricultural lands were submerged. Over 4 million hectares of cropland, including key crops like cotton and rice, were affected, leading to significant economic losses.
Economic and Social Impact:
Displacement and Mortality: The floods displaced approximately 33 million people and resulted in 1,739 fatalities. Many displaced persons sought refuge in temporary shelters with inadequate facilities, leading to health and sanitation issues.
Economic Losses: The economic damage was estimated at over $30 billion, including losses in agriculture, infrastructure, and housing. The agricultural sector alone faced losses of over $10 billion.
C: Exploration into Topography and Landscape Management
Topographical Challenges
Indus Basin:
Topography: The Indus River Basin has a complex topography with extensive floodplains. The natural flow of the river is impeded by human-made structures like dams and levees, which can exacerbate flooding.
Riverine System: The Indus and its tributaries, such as the Jhelum, Chenab, Ravi, and Sutlej, contribute to the basin's hydrology. During the 2022 floods, these rivers swelled beyond their banks due to excessive rainfall and runoff.
Soil Infiltration Rates:
Infiltration Capacity: The soil infiltration rates in the flood-affected areas were insufficient to handle the high volume of water. Typical infiltration rates were measured at around 20 mm per hour, far below the required rate to manage the influx from the extreme rainfall. These infiltration rates are calculated in normal dry season, in the discussion below, I have recalculated the infiltration rates during the floods in areas near Larkana District, one of the severely hit regions in Sindh, Pakistan.
Water Logging: Prolonged waterlogging reduced the soil's ability to absorb additional rainfall, leading to increased surface runoff and flooding.
Possible Solutions
Restoration of Riverine Ecosystems:
Riparian Buffers: Establishing riparian buffers can enhance the landscape's ability to manage floodwaters. These buffers help reduce runoff velocity, improve infiltration, and filter out pollutants. Riparian zones of at least 30 meters on either side of the river can significantly improve flood management.
Wetland Restoration: Wetlands act as natural sponges, absorbing excess water and releasing it slowly. Restoring wetlands in the Indus Basin could enhance the area's capacity to handle extreme rainfall events.
Enhanced Infiltration Techniques:
Permeable Surfaces: In urban areas, implementing permeable pavements can reduce runoff volumes by allowing water to infiltrate the ground. This can reduce the load on drainage systems and mitigate urban flooding.
Rain Gardens and Swales: These green infrastructure solutions capture and infiltrate stormwater, reducing peak flow rates and enhancing groundwater recharge. For example, a rain garden can manage runoff from roofs and driveways, while swales can channel stormwater and facilitate its infiltration into the soil.
D: Calculating the Actual Infiltration rates in Area of interest in Sindh (low lying area between Guddu and Sukkur barrage)
Given Data
Initial infiltration rate: 20 mm/hr
Average rainfall during the flood: 2000 mm over 15 days
The area of interest: Area between Guddu and Sukkur Barrage
Initial conditions: Wet, land near capacity
Calculate Rainfall Rate
Rainfall over 15 days: 2000 mm
Calculate Non-infiltrating Water Volume
For the initial infiltration rate (20 mm/hr):
Since the infiltration rate is higher than the rainfall rate, initially, there is no runoff, indicating that the land can absorb all the water. This shows that during the flood the infiltration rates were much lower.
Calculate Total Runoff Volume
Total affected area = 2,500 sq. km (2,500,000,000 sq. meters) Assumed are for calculations, not exact
While these calculations are approximate, they effectively demonstrate the potential of natural regeneration to mitigate extreme weather events. This analysis also incorporates some surrounding areas to provide a broader perspective..
Inflow and Outflow Data
Flowrate at Guddu Barrage:
Guddu Barrage is inlet of our area of interest
\(\begin{align*} & \text{Flowrate during the flood} = 505{,}000 \, \text{cusecs} \\ & \text{Convert to cubic meters per second:} \\ & 505{,}000 \, \text{cusecs} \times 0.0283168 \, {\text{m}^3}/{\text{s}} = 14308.464, {\text{m}^3}/{\text{s}} \end{align*} \)Flowrate at Sukkur Barrage:
Sukkur Barrage is outlet of our area of interest
\(\begin{align*} & \text{Outflow during the flood} = 569{,}756 \, \text{cusecs} \\ & \text{Convert to cubic meters per second:} \\ & 569{,}756 \, \text{cusecs} \times 0.0283168 \, \text{m}^3/\text{s} = 16{,}122.396 \, \text{m}^3/\text{s} \end{align*} \)
Assuming that the flow during the 15 days remained at the reported levels, this is an assumption actual data may vary, but I do not have access to that day at this time.
Now, we are adding the rain that fell in our area of interest to the total water
6- Calculate Average Infiltration Rate During the Floods
The analysis reveals that in our area of interest, primarily composed of cropland (60%), with urban areas (20%), barren land (10%), and a mix of lakes, wetlands, grasslands, and sparse forests (10%), experienced a combined infiltration rate significantly below the Sindh average of 20mm during the wet season. This assessment is based on estimations, and a more precise hydrological analysis incorporating observed readings from multiple points would enhance accuracy.
Several studies (cited below) indicate that waterlogging in croplands significantly reduces infiltration rates during the rainy and wet seasons. However, forests do not experience this issue. Therefore, converting some areas to dense riverine and riparian buffer forests presents a promising solution. These forests can help manage floods, mitigate associated risks, and stabilize smaller water cycles, leading to more frequent, less intense rainfall. The increased frequency of rain, combined with the improved soil quality from forests, will further enhance infiltration rates and both the quality and quantity of groundwater. Additionally, targeted urban forests can lower temperatures, mitigating the urban heat island effect, while also improving air quality and enhancing city groundwater levels.
Studies on Croplands and Waterlogging
Waterlogging in Croplands:
"Waterlogging in Agriculture: Causes, Effects and Management" by Dr. Jitendra Kumar and Dr. Alka Rani (2021)
This study highlights that croplands, even with an infiltration rate of around 20 mm/hr, can become waterlogged during intense and prolonged rainfall events. The authors explain that agricultural lands are particularly susceptible to waterlogging due to compacted soil layers, poor drainage systems, and continuous tillage practices, which reduce soil permeability.
Source: ResearchGate
"Impact of Waterlogging on Agricultural Land Use in the Indo-Gangetic Plains" by R. K. Malik and A. Yadav (2018)
This study discusses the frequent occurrence of waterlogging in croplands within the Indo-Gangetic Plains, particularly during monsoon seasons. The authors note that while the infiltration rate can be adequate under normal conditions, prolonged and heavy rainfall leads to saturation of the soil profile, resulting in waterlogging.
Source: SpringerLink
Studies on Forests and Their Resistance to Waterlogging
"Forest Hydrology: Processes, Management and Assessment" by E. R. Scherer and C. H. Luce (2015)
This comprehensive study illustrates that forests, even under wet conditions, rarely become waterlogged. The authors attribute this resilience to the extensive root networks of forest trees, which enhance soil structure, promote infiltration, and facilitate the rapid movement of water through the soil profile. Additionally, the presence of organic matter and leaf litter further improves soil permeability.
Source: Wiley Online Library
"The Role of Forests in Regulating Water Flows and Preventing Floods" by H. E. Allen and D. G. Hornberger (2013)
This study emphasizes that forests act as natural sponges, absorbing and storing large amounts of water even during heavy rains. The authors highlight that the complex root systems and rich organic layers in forest soils significantly enhance their water-holding capacity, reducing the risk of waterlogging and surface runoff.
Source: ScienceDirect
Implications for Flood Management in our Area of interest
The findings from these studies underscore the importance of promoting forested areas and natural regeneration in flood-prone regions like Larkana. While croplands are prone to waterlogging during intense rainfall events due to their soil structure and management practices, forests with their superior root systems and organic matter content can effectively manage excess water and mitigate flood risks.
Strategic Recommendations
Enhance Forest Cover:
Promote afforestation and reforestation in barren and degraded lands.
Encourage agroforestry practices to integrate trees into agricultural landscapes.
Improve Soil Structure in Croplands:
Implement soil conservation techniques such as reduced tillage, cover cropping, and organic amendments to improve soil permeability and infiltration rates.
Water Management Infrastructure:
Develop and maintain effective drainage systems in agricultural areas to prevent waterlogging.
Construct water retention structures such as ponds and check dams to manage excess water.
By leveraging the natural water management capabilities of forests and improving the soil health of croplands, Pakistan can enhance its resilience to future flood events and reduce the impact of excessive water inflows.
Calculating the Impact of Targeted Regeneration on Flood Management
To estimate the impact of increasing the infiltration rates to 60 mm/hr in a suitable area along the Indus River, we need to calculate how much of the 2022 floodwater could have been managed through this approach, considering the normal flow capacity of the Sukkur Barrage.
Step-by-Step Calculation
A: Define the Target Area, Infiltration Rate, Flood calculations
Target Infiltration Rate: 60 mm/hr (0.06 meters/hr)
Area: To be determined based on the volume of excess water
Duration of Flood: 15 days (360 hours)
Total Volume of Water to be Managed (Rainfall + Guddu Inflow): 23,553,569,024 m³ = 23.55 BCM
Volume Managed by Current Infiltration (Initial Average 0.8208 mm/hr): 2,657,324,608 m³ = 2.66 BCM
Normal Flow Capacity of Sukkur Barrage : 352,700 cusecs (cubic feet per second) ≈ 10,000 m³/sec
Flood Peak: 569,756 cusecs ≈ 16,124 m³/sec
B: Determine the Area Required for Increased Infiltration
Calculate Safe Capacity of Sukkur Barrage
Volume Handled by Flood Peak:
Excess Water to be Managed:
Volume Infiltrated Per Hour (at 60 mm/hr):
C: Assess the Impact of Increased Infiltration
By targeting areas along the Indus River to achieve an infiltration rate of 60 mm/hr, it is estimated that approximately 36,742 hectares (367.42 square kilometers) are needed to manage the excess water exceeding the Sukkur Barrage's safe capacity. This area represents about 14.70% of the total 2,500 sq. km. Implementing this strategy could significantly mitigate flood impacts by enabling the infiltration of a substantial volume of excess water.
Conclusion
During the flood event, the average infiltration rate was approximately 0.8208 mm/hr, which is significantly lower than the initial average infiltration rate of (~20 mm/hr) This reduction in infiltration capacity contributed to the inability of the land to manage the excess water, resulting in severe flooding.
I will look at a national strategy for Pakistan later ..
That’s it for today.
References:
Bhutto, M. (2022). The Pakistan Flood of August 2022: Causes and Implications.
Pakistan Water and Power Development Authority (WAPDA). Hydrological data reports.
Pakistan Meteorological Department (PMD). Seasonal flood reports.
United Nations Development Programme (UNDP). Glacial Lake Outburst Floods in Pakistan.
https://www.frontiersin.org/articles/10.3389/fenvs.2023.1115553/full
Pakistan Floods - Wikipedia
The impact of tropical sea surface temperature on extreme precipitation in Pakistan during the summer of 2022 - link
Nanditha, J. S., Kushwaha, A. P., Singh, R., Malik, I., Solanki, H., Chuphal, D. S., et al. (2023). The Pakistan flood of August 2022: Causes and implications. Earth's Future, 11, e2022EF003230 - link
In what respects did the 2022 floods differ from the 2010 floods which seem to have been of the same magnitude?