Off-road at the edge of a desert

We were on a long straight road to the weird desert of Kutch. The main highway was in very good repair, and allowed us to make good time. The dawn was still pink in the sky when we left Ahmedabad, and even after a leisurely breakfast and a detour through Nal Sarovar for Sociable Lapwings, it was well before noon when I noticed how dusty the surroundings were.

There were still cultivated fields by the road, but you only had to look at the sky to see the dust. Directly overhead the sky was a clear blue, but if you let your eyes fall towards the horizon you could make out the grey of suspended dust. I had brought along a packet of surgical masks to protect me against this desert dust, but eventually it turned out to be inadequate. The next time I come this way I will have to bring along a sturdier mask with a good filter.

The moment you go off-road, everything changes. The irrigated edge reveals itself as a tiny intrusion. This is the kingdom of dust. Clumps of woody bushes grow here and there, and get more sparse as you penetrate deeper into the desert. Here at the edge of the Rann of Kutch, there are ponds, but even at the edge of the pond there is no grass. Taming this desert will require finding a grass to hold the topsoil together.

In the last year I’ve begun to see the desert as an exercise for the future. This part of India does not get monsoon. The popular understanding is that this is because the monsoon winds are “depleted of moisture” by the time they reach Gujarat and Rajasthan. This is false. The desert is very close to the sea, and right in the path of direct monsoon winds. These are kept away by a high-pressure system which sits over West Asia. In future if the monsoon wind system slackens due to the warming of the oceans, then this high pressure zone will expand, and the desert will begin to move eastwards. Finding a way to keep the topsoil from crumbling into dust is therefore an insurance against the future.

We pass villages where dust has piled up against structures, a graveyard is in the process of being buried again. I wondered about this village, which seems to have been abandoned rather recently. I saw a large house, with the roof caved in, walls still standing. Behind it was a shady tree which brought back memories. When I was a child, growing up in north India, courtyards of each house would have one or two such trees. Learning to climb them was one of the rites of passage for youngsters. In north India the courtyards and trees are gone. Here the trees remain, but people are gone.

The making of the Thar desert

As we drove through the Thar desert, I wondered about the mysterious landscape around me. India receives so much rainfall from the monsoon that it is hard to believe that it contains a desert. The popular belief that the monsoon winds are “depleted” of moisture by the time they reach the desert is false. The distance to the sea is rather small, and the air is generally moist. In just three winter months, when the rest of India is dry, the amount of water deposited by dew in the desert is between 30% and 40% of the total rainfall. Something prevents the western branch of the monsoon from penetrating into Gujarat and Rajasthan.

It is believed that this is the immense high-pressure anti-cyclone that exists over the Sahara and West-Asian desert. In fact, the claim is that the monsoon winds prevent the spread of this pattern to the rest of India. Evidence for competition between the two systems is what happens when a third factor occasionally intrudes. In the infrequent episodes when a Western disturbance hits India during the monsoon, causing immediate heavy rainfall and flooding over a wide area of the desert. This means that the monsoon winds are not depleted of moisture in this region, but are obstructed from flowing by the anti-cyclone. If this conjecture is true, then a weakening of the monsoon due to climate change could allow the anti-cyclone to extend across India, making it an arid habitat.

Our jeep had long wandered off the road. The flat landscape that I’d grown used to gradually gave way to undulations. There was still a strong wind blowing dust and sand into my face, so I had my mask on. But when I looked around, the ground had changed. Until a minute ago we were driving through hard packed sand (see the featured photo). Now, all around us I could see something different poking through the sand. The photo above shows the surface. The broken flat stones are made of a material called calcrete. This is formed by the action of water and atmospheric carbon dioxide on wet dust and sand (the word calcrete seems to be a portmanteau of calcium and concrete). The presence of calcrete means that wet lands turned to desert at some time in the past. Dating of calcrete in the Thar desert shows repeated cycles of wetness and desert starting from 1.5 million (15 lakh) years ago to 250,000 years ago.

I walked across this landscape in search of a wheatear, but my attention was on the landscape. A short walk through sand brought me to something that looked like a dry riverbed into which sand had trickled: calcrete was overlain with sand, as you can see in the photo above. Aerial and satellite photography shows evidence for a well-organized drainage system of interlinked rivers in the far past, disrupted by climate change. Successive surveys and dating showed brief re-emergence of local drainage systems over a period of a million years, which were disrupted within a few tens of thousands of years.

The wheatear perched briefly on a bush and I managed to take a photo. After it had flown off, I looked at the land behind the bush (photo above) and it became obvious that it had been shaped by flowing water. The surface was covered in calcrete, which it why it had not been reshaped by the wind. Studies of pollen around Didwana lake in the eastern part of the desert have established that about 6500 years ago the area was wet enough to support a large variety of grasses and flowering herbs and shrubs, of the kind which are usually pollinated by butterflies. This dried up around 4000 years ago. When these studies were first published, there was speculation in the press about the connection with the mythical river called Saraswati. More studies revealed a fluctuating boundary of the desert over human history and pre-history. Palaeolithic tools and sites have been found buried intact in the sand, showing that the desert shifts fairly abruptly. The gradual abandonment of Harappan cities could also have been partly due to such climate fluctuations.

The bird gone, I climbed a little bluff to join The Family, and saw immediately clear evidence that I had walked across the bottom of an ancient river. The photo above makes it very clear. How old was this? I’m sure it has been mapped out. The geological and climatic history of the Thar desert has been examined in great detail in the last 60 years by a large number of scientists working in India. There is a group in IIT Mumbai who examined the age of sand dunes, and found some as old as 160,000 years, and others as young as 11,000 years. In several of the photos above, you can see distant dunes. It gives me shivers to realize that they were being laid down at the same time as glaciers advanced across the north of Europe, Asia and the Americas. As water got locked up in ice, this part of the world turned dry.

Geology and climate sculpt the land over periods longer than our lives, even longer than our civilizations. As a result, it has been hard to see the forces which shape our societies. Walking across that river bed I thought that I had a tiny view of these forces. In the past our actions have been too weak to shape the planet. No longer. We need to understand the Thar desert to plan a way ahead as the climate changes.

A sedentary acrobat! Really?

Several times in my forays into Pench National Park, I noticed a bright blue flash of wings at the edge of dusty meadows full of dried grass. If I’d seen this colour near a pond or soak, I would have thought of a kingfisher. But in this habitat it was the Indian roller bird, Coracias benghalensis. True to its name it twisted and rolled in soaring flight each time I saw one. The spectacular flight is a mating display; something that is visible during its breeding season, between March and July. Unfortunately, the camera I had with me compensates for its enormous zoom by an equally enormous shutter lag. This rules out taking photos of such displays.

In any case, I was at first very surprised to find a paper which reported that roller birds were observed to spend 90% of their time sitting, at all hours of the day. It seems that foraging and feeding took substantially less than 10% of its waking hours. Such a lucky bird!

The time spent foraging may depend on the kind of terrain the bird is seen in. In the agricultural land where the study was performed, rollers were found to eat insects almost exclusively. However, in the wild it is known to prefer lizards and frogs, and sometimes is even seen eating small snakes. The larger prey may keep the bird full for a longer time, but it may also change the amount of time spent foraging before it feeds.

On second thought, I should not have been very surprised when I found that the roller is a sedentary bird. After all, I have so many photos of a roller perched somewhere (the photos here are examples). Indian roller bird in Pench National ParkOnce you get one in your viewfinder, you can go on taking photos to your heart’s content. With its wings closed it will seem to be largely reddish brown, with the blue colouring appearing only on the head, tail and part of the chest. In the 1930s, the Indian physicist C.V. Raman studied the blue colour of the roller’s wings and found that the colour was due to double scattering of light from the feathers of the bird, and not from a pigment. He moved on to study the blue colour of the sea, and won a Nobel prize for that work. Today, the nano-structures on the feathers of the roller that produce the colour are very well understood.

The Indian roller is not a threatened species. It is seen over all of India and south-east Asia, and westwards along the Arabian sea and the Gulf of Iran. Dedicated bird-watchers ignore sightings of the roller, and would roll their eyes if they saw me taking photos of one. But recent fossil finds suggest that about 30 million years ago its ancestors were spread even more widely across the world. Ancient climate changes then seem to have restricted the populations of roller birds to (roughly) their present geographical range. There are such wonderful histories behind every bird!

The post-extinct Elephants

I read in a document from the Zoological Survey of India that the Ain i Akbari mentions wild elephants in the area that the Pench National Park now occupies. These annals of the reign of the Mughal emperor Akbar were written in the 16th century CE. I looked at my copy. Pench gets no mention, of course, but a larger geographical area around it is said to have these beasts. The ZSI document goes on to say that books from the 18th century about this area no longer mention these animals. The document concludes that elephants must have gone locally extinct in these centuries. It is interesting that the temperature minimum of the Little Ice Age occurred roughly at this time. This caused changes in rainfall patterns, and resulted in a sequence of droughts during the 18th century. Could it have been climate change of this kind that caused the extinction of the local population of elephants in this region?

Elephant patrol in Pench National Forest

So it is a little surprising to see elephants in the jungles of Pench, until you realize that there are only five elephants, and they are domesticated. The forest department uses them to patrol the jungle, especially areas which are otherwise hard to reach. We were in the usual open jeep when this patrol passed by. Our driver asked about tigers, and one of mahouts said that he’d seen one nearby and it might come down to drink water shortly. It didn’t. As they talked, I saw the elephant break one large branch off a small tree and munch on its leaves.

Intrigued, I searched for elephants in Pench and found the following paragraph in a book for a former forest ranger, R. C. Sharma, in a book called "The Wildlife Memoirs, a Forester Recollects".

R.C.Sharma, memoirs

This is a possible clue how climate change could eventually lead to disastrous denudation of flora, which cause large herbivores to die out. I’m sure an event like this has cascading effects through the whole ecosystem. The landscape that we see in Pench today must have been shaped by the climate of three centuries ago.