When floodwater enters a village, one of the first questions rescuers need answered is surprisingly simple: Where is the water, and who is still there?
From the ground, finding that answer can be difficult. Roads may be submerged, bridges damaged and entire neighbourhoods cut off. A rescue team may know that a village is flooded, but not which roads are still passable, which homes are surrounded by water or where people are stranded.
This is where a small flying machine can offer a very different view.
During the recent floods in Gujarat, Mehsana-based Prime UAV deployed drones in Dholka, Ahmedabad, to support rescue teams. With some areas inaccessible to tractors and boats, the drones provided aerial surveillance, including at night, and helped teams identify areas where people needed assistance.
They were also used to deliver food and water packets in waterproof payload boxes to locations that were difficult to reach by road.
But how does a drone turn a flooded landscape into information that rescuers can actually use?
First, it gives rescuers a view from above
Think of a drone as an extra pair of eyes in the sky.
Instead of sending people into potentially dangerous floodwater to inspect every road and house, a drone can fly over an affected area and capture detailed images using cameras and other sensors.
During a flood, drones can do more than survey the damage — some can carry food, water and essential supplies to people cut off by rising water. Photograph: (AI generated)
These images can then be processed using specialised software to create an orthomosaic map — a large, detailed aerial map made by combining hundreds of overlapping photographs.
With repeated flights, teams can also track how the flood is changing: where water is spreading, which roads have disappeared underwater and which areas are becoming accessible again.
So, where does the “mapping” happen?
The useful part is not just the drone flying. It is what happens to the information it collects.
A drone can capture overlapping photographs along a planned flight path. Mapping software identifies common points across those images and combines them into a single map.
For more detailed surveys, drones can also use technologies such as LiDAR and RTK GPS.
LiDAR uses laser measurements to map the shape and elevation of terrain. RTK GPS can provide highly precise positioning, helping place captured images and measurements more accurately.
Put simply, the camera shows what is there, while mapping and positioning technologies help establish where exactly it is and, in some cases, how high or low the land lies.
That information can be particularly useful in flood-prone areas, where understanding terrain, drainage channels, embankments and floodplains can help authorities prepare for and respond to flooding.
Before a flood: building a clearer picture
Drones do not have to wait for a disaster to strike.
By stitching together hundreds of aerial photographs, drones can turn a flooded landscape into detailed maps that show rescuers what has changed and where.
Photograph: (Instagram/ @garudaaerospace)
Before the monsoon, aerial surveys can document rivers, drainage channels, embankments, bridges and other infrastructure. Detailed terrain maps can help identify low-lying areas and provide a better understanding of how water could move across a landscape.
The real value is having a before picture.
Once a flood occurs, that earlier map can be compared with fresh drone imagery to understand what has changed.
During a flood: helping teams find people and plan rescues
This is when the technology can become particularly useful.
Drones can survey large or dangerous areas, identify flooded roads and damaged infrastructure, and give emergency teams additional information when deciding where to send rescue personnel and supplies.
Depending on the equipment being used, thermal cameras can also help detect heat signatures during search-and-rescue operations.
Payload-carrying drones can deliver essentials such as food, water or medical supplies to locations that rescuers cannot immediately reach.
Importantly, drones are not a replacement for boats, rescue workers or helicopters. Their role is to provide another layer of information, helping those teams understand the situation before and during an operation.
After the water recedes: the map still matters
A drone’s job does not necessarily end when the floodwater goes down.
Fresh aerial imagery can help document damage to roads, bridges, buildings, embankments and agricultural land. Engineers and authorities can use this information to assess damage, plan repairs and identify areas that may need stronger protection before the next flood.
Even after the waters recede, aerial imagery can help document damaged infrastructure and guide recovery, repairs and future flood preparedness.
Photograph: (LinkedIn/@OEA Consults LTD)
Over time, these aerial records can also provide a visual history of how a particular area has changed and responded to flooding.
That is perhaps the most useful way to look at drones in disaster response.
A flood can change a landscape within hours. For rescuers on the ground, understanding those changes quickly can make a difficult situation easier to navigate.
By giving emergency teams a clearer view of what is happening below, drones can help turn aerial data into better-informed, faster action when it matters most.
