I left Sylhet in January 1998 for higher study at the National University of Singapore (NUS). On the very first day at NUS I was so amazed by the undulating view of the campus where even a minor variation in natural topography was conserved. It took me around six months to get familiar with the route from my laboratory to the department premises just few buildings away -- 6th floor of one building connected with the ground floor of another building and then 3rd floor of another. They could easily flatten those hillocks, instead kept them intact. The same I found in Japan or Switzerland or even Malaysia -- cautiously preserved natural topography.

Well, what was happening in Bangladesh at that time? While staying abroad I used to keep in touch with SUST colleagues, but utterly shocked to know that hill cutting was continuing unabatedly in Bangladesh and even at a faster rate. Very frequently I used to encounter newspaper stories through internet on such massive destruction of hills along Sylhet as well as Chittagong and Hill Tracts region. More shocking was that the administration was not taking any attempt to stop it.

In 2004, we presented a paper at an international symposium held in Dhaka on the topic and the paper was highly appreciated by the conference attendees including foreign delegates. In 2006, we published an international journal paper on our research entitled Destroying Hills Along the North Eastern Part of Bangladesh: A qualitative Assessment of extent of the Problem and its Probable Impact.

Now, when I see those ill-fated dead bodies of Cittagong tragedy, it seems to me that all of our tireless efforts were actually futile. Probably it is our national characteristic that we are always reactive rather than proactive. In many other cases, even about those clearly visible environmental problems of Dhaka city we are showing almost same the attitude -- unless Dhaka is sunk we will not take any action to repair its drainage system or restore those water bodies, unless and Dhaka is subsided probably we will not take any action to stop withdrawing groundwater, any unless a severe earthquake hit and the country and millions of people die probably we will not realise that we are living a highly vulnerable earthquake zone where two converging plate boundaries are very close to us, and above all we will not stop unplanned urbanization in Dhaka unless it turns to be a big squatter or concrete jungle. Actually we cannot resist our temptation to destroy all of these delicate balances in nature unless it takes revenge destroying us.

I cannot understand the reason for such attitude -- we rarely listen to experts, rather the country is led by bureaucrats of general knowledge. This is the age of specialisation, but our decision making process rarely includes specialists. Well, even if now, at the cost of 120 lives, government takes some serious actions, one would be happy. But we are afraid probably within few days all these will fade out until another land slide takes say, 240 lives.

After the Chittagong tragedy everybody is talking about the consequence of hill cutting. I just like to confirm that landslide is just one of the numerous consequence of cutting hills a short term effect. Apart from this, a number of long term far reaching effects are there which can gradually destroy the ecosystem, affect river regime, regional climate and biodiversity. This write-up tries to summarise the technical issues in simple language based on the journal paper already published. The study is based on the data and information collected along the Sylhet region. No doubt like Chittagong, Sylhet is going to be the next target for disaster related to hill cutting.

Extent of the problem
It is estimated that every year about 10-12 percent of the total hills and hillocks are cut or destroyed along Sylhet region. The types of such destruction varies in forms like simply uncovering of hills from their natural vegetation and replace it with new types of crops or trees, or in an extreme case of completely destroying it and flattening the lull for residential, agricultural or in other development purposes. Like other regions, the vested interest of rich and powerful local land grabbers in collaboration with corrupt elements of district administration is mostly the culprit. However, poor people, especially those migrated from other districts are also liable in some cases.

Impact
Among the topographical features of the region, hills are the most dominating one contributing to the delicate balance in the ecosystem. Heavy rainfall, tea garden, dense bamboo and cane bushes, high flood plain and the flashy rivers, all the features are intimately related and contributed by the hills. It is obvious that any sort of mishandling of the hills will make the ecosystem of this region complicated.

Effects on ecosystem and biodiversity: Destruction of hill affects indigenous flora and fauna. As the direct effect of hill cutting, natural vegetation covers including trees and grasses over the hills are gone. On the other hand, the fertile topsoil with enriched nutrient and biomass are removed. Further growth of plants and trees from the cut portion of the hill thus retarded or takes long time. Such deforestation can change the microclimatic condition of the region like rainfall, temperature, wind velocity, etc and also lead to soil erosion removing top soils which will further retard plant growth.

Likewise, hill cutting will affect different species living there disturbing their movement and shelter, killing some or pushing them away. As a consequence their interdependency for food or food chain will be disrupted and many species will be endangered. It has been already noticed that many species of forest animals have become rare in the Sylhet region. Tigers are almost lost or rarely seen, different types of monkeys are also endangered.

Chances of earthquake will increase: Depending on its geographical location, both Sylhet and Chittagong are highly prone to earthquake. Most of the earthquakes in the world occurred along the fault lines of the tectonic plates. As it is evident the Eurasian plate and the Indo-Australian plate meeting line passes just along the east and north boundary of Bangladesh. Chittagong and Sylhet, the two regions are at a very close distance from the fault line and thus highly susceptible to earthquakes. Bangladesh National Building Code has already ranked Sylhet and Chittagong as the highest risk zones for earthquake.

Destruction of hills along such sensitive zones will obviously aggravate earthquake risk as it will leave some sorts of imbalance in earth pressure. Even though there is no literature on such incidents, however, almost same incident is noticed at different parts of the world. For instance, construction of large dam along the mountainous region found to increase intensity of earthquake occurrence due to pressure change from excess water storage. Hill cutting issue can be considered as analogous to it and highly possible.

Reduction in the intensity of rainfall: For precipitation, lifting of moist air mass is necessary for condensation into droplet and cloud formation. In this case hills act as a helpful barrier, where the moist air, after being obstructed, lifts upward and gradually condenses to form cloud, which is termed as orographic precipitation. This is the main reason for high intensity of rainfall in the Sylhet region. Due to destruction of hills, now moist air will not be obstructed as before and the amount of rainfall in Sylhet region is likely to decrease. The phenomenon has already been proved as the average yearly rainfall over the Sylhet region has decreased. This will result in a massive change in the eco-system of tea plantation, which requires heavy rainfall. On the other hand, the moist air that blows from south will now move to the northern hilly region Meghalaya of India.

Soil erosion and landslide: After precipitation, water from different places comes to the nearest rivers, channels, etc which is called runoff. Forests or vegetation cover of the land surface make this runoff movement slower with high infiltration and less erosion of soil. On the other hand, runoff from deforested surface is much higher due to less obstruction of from vegetation resulting in higher erosion which in the long run will decrease the recharge of ground water. Lowering ground water table has already been detected in some experiments by the Public Health Engineering Department of Sylhet.

Siltation in rivers and canals: The eroded soil ultimately comes into the rivers and wetlands with runoff. Here it gradually starts to settle, reducing the effective capacity of water bodies to hold water. Huge siltation has already become a big problem for our rivers, especially the rivers in Sylhet region. The frequency of floods in monsoon period thus increases and reduces the storage capacity of rivers in dry season. Most of the hilly channels along Sylhet city or nearby areas are already blocked due to such siltation. Likewise, some canals along Chittagong including Chaktai Khal are also silted by such eroded soil. Soil quality of the hilly region of Bangladesh is mainly acidic. So, the eroded soils will turn water acidic as well. Wetlands like Haor and Bills, etc may also be affected because of siltation and water quality problem. Haors along Sylhet region are considered as highly valuable in ecological importance with a vast reserve of aquatic flora and fauna, which are already started to suffer from problems like these.

Change in catchment drainage and flush flood: The region from which a river collects its water after rainfall is known as its catchment. For a particular river, catchment is determined from the land slope. Normally the hills act as divide between two river catchments. Now if the hills are cut, then the land slope pattern and divide would change resulting in changes in water availability at different rivers and channels. On the other hand, river cross-sections build up based on the catchment pattern and the amount of rainfall over it. As mentioned, if rainfall in Sylhet region decreases and increases is Meghalaya region, them for the upstream sections of the rivers in the Sylhet region this excess flow will appear as unusual to the capacity of the river cross sections, causing flash flood. Also deforestation and resulting accelerated soil erosion, which increases the sediment load of rivers, will boost the magnitude of floods.

From the above discussion it is clear that indiscriminate destruction of hills can result in drastic consequences threatening life and properties. So what should we do? Keep all those hills intact? Probably it is not possible. In a lowlying country with ever-increasing population there will always be increased pressure on those highlands. Again if sea level rises by one meter, probably we will have no option but to take shelter on those highlands! Well, developing highlands or hilly region is not rare in the world. In many countries of the world most of the people live in mountainous areas. The things that need to be ensured here is to be aware of all those implications mentioned above and take technically sound measures accordingly. There should be always trade-off between conserving and exploiting nature. In many cases we are motivated by early profits because of ignorance and lack of understanding about the cause and effect relationship in the long term. The concept of sustainable development emerges here. Where to develop and how to develop should be decided based on sound scientific studies.

Dr. Md. Sirajul Islam, is an environmental engineer and Assistant Professor, Department of Environmental Science and Management North South University.